Family XLI. Phractopeltida, Haeckel (Pl. , figs. 1-6)

Phractopeltida, Haeckel, 1881, Prodromus, p. 468.

Definition.—Acantharia with double spherical lattice-shell, composed of the branched apophyses of twenty radial spines meeting in its centre, and disposed according to the Müllerian law of Icosacantha. Central capsule spherical, enclosing the inner and surrounded by the outer concentric shell.

The family Phractopeltida differs from all other Acantharia in the development of a double spherical shell, composed of two concentric lattice-spheres, which are united by twenty radial spines meeting in the common centre. We could therefore oppose the Phractopeltida as Diplophracta to all other Acanthophracta as Haplophracta (with simple shell). The former exhibit a relation to the latter, similar to that exhibited by the Dyosphærida to the simple Monosphærida among the Sphæroidea.

In my Monograph (1862, p. 423) I described only one genus appertaining to this family, Aspidomma. I founded it upon the singular Phractopelta, described by J. Müller as Haliomma hystrix. A second species of Aspidomma, the Acanthometra mucronata of J. Müller, was probably an Astrolonche. At that time I placed Aspidomma among the Haliommatida, led by the erroneous opinion that it might represent a transition-form between Dorataspis and Haliomma. But I afterwards gave up this view, as I was convinced that there is no true phylogenetic connection between the acanthinic Dorataspida (Actipylea) and the siliceous Haliommatida (Peripylea). Therefore in my Prodromus (1881, p. 468) I placed Aspidomma among the Dorataspida and changed its name to Phractopelta, to avoid further confusion with the unrelated Ommatida (Sphæroidea). It formed there, with three nearly related genera, the "subfamily Phractopeltida," which we now advance to the higher rank of a separate family. (By a typographical mistake the words are printed in the Prodromus Phractopelma and Phractopelmida, &c., instead of Phractopelta and Phractopeltida, &c.). The detection of other new species appertaining to this family, and a closer anatomical investigation of them, has now led to the distinction of five different genera, characterised by other differences than were employed in 1881 in the provisional system of the "Prodromus."

The two concentric spherical lattice-shells of the Phractopeltida, connected by radial beams, correspond perfectly to those of the double-shelled Dyosphærida (Haliomma, Diplosphæra, &c.), and in both cases we may call the smaller inner the "medullary shell," and the larger outer the "cortical shell." There is no doubt that the double-shelled Phractopeltida must be derived phylogenetically from the simple-shelled Dorataspida (just as we derive the double Dyosphærida from the simple Monosphærida). But it is not yet possible to decide positively which of the two shells is the first formed. Probably the small inner or medullary shell of the Phractopeltida is the first formed, and corresponds to the simple spherical lattice-shell of the Dorataspida; and the larger outer or cortical shell of the former is a later new formation, absent in the latter family. This opinion seems to be confirmed by the genus Orophaspis, the only form among the Dorataspida, in which the radial spines outside the shell bear free latticed apophyses. If these twenty apophyses grow further and meet one another, the second or outer shell of Phractopelta may be formed. But some objections may be raised to this opinion from the peculiar structure and the very small size of the inner shell; and there is some possibility that this latter is a secondary later product inside of the primary cortical shell. The probably phylogenetic series which reveals the origin of the Phractopeltida is the following:—Acanthometron, Zygacantha, Lithophyllium, Phractacantha, Doracantha, Dorataspis, Orophaspis, Phractopelta.

The twenty radial spines exhibit in all Phractopeltida the same characteristic position and relation as in all other Icosacantha, and are constantly arranged according to the Müllerian law in four meridian planes, their distal ends falling into five parallel zones. Their distinction in the majority of the Phractopeltida is not difficult, since the spines of the different zones bear apophyses of different shapes. Sometimes the four equatorial spines are stouter than the sixteen other spines, and often the eight tropical spines are somewhat different in form from the eight polar and from the four equatorial spines. The length of all twenty spines is commonly equal. Their form is usually more or less compressed, two-edged (as in Zygacantha), more rarely cylindrical (as in Acanthometron), or somewhat quadrangular (but not truly prismatic); therefore the transverse section of the spines is commonly elliptical or lanceolate, rarely circular or rhombic, never square; this seems to indicate their origin from Zygacantha. As in all Acantharia, the spines consist of acanthin, not of silex. Their central ends are either perfectly grown together, and form a single star of acanthin, or the triangular faces of their small pyramidal bases are supported one upon another, without true concrescence.

The apophyses of the radial spines, by which the two concentric spherical shells are formed, seem to be constantly four on each spine, two being opposite in each shell. The proximal pair of opposite apophyses, forming the inner or medullary shell, is constantly much smaller than the distal pair composing the outer or cortical shell (Pl. , fig. 5). The proximal pair corresponds probably to the two primary apophyses of the Diporaspida (Phractaspis, Dorataspis, &c.), whilst the distal pair corresponds to the free apophyses of Orophaspis (Pl. , fig. 6). Therefore the Phractopeltida may be derived phylogenetically from the Diporaspida (not from the Tessaraspida). In the common ancestral genus of this family, Phractopelta, the free part of the radial spines (outside the outer shell) is quite simple, without free apophyses; in all other genera of the family that free part of the spines (either in all twenty spines or only in some of them) bears a third pair of lateral apophyses; these may be either simple or branched or even latticed; but the outer apophyses (of the third rank) remain constantly free, and a third lattice-shell is never formed by union of their edges (Pl. , figs. 2-4).

The inner lattice-shell of the Phractopeltida, or their "medullary shell," is constantly very small (commonly 0.03 to 0.05 mm. in diameter, rarely more). Its structure is difficult to make out; in the unbroken shell it is concealed by the dense network of the outer shell; in the broken shell it is commonly destroyed. Usually the pores of the inner shell are very small, circular or subcircular, scarcely as broad as the small separating bars. In the majority of Phractopeltida their number seems to be about forty, being probably the forty primary aspinal pores of the Diporaspida; in some species this number seems to be exceeded, so that perhaps some sutural pores may exist between the aspinal pores; but commonly the twenty plates composing the inner shell (each with two aspinal pores) seems to grow together perfectly by their meeting edges, so that there are no sutural pores between them. Evident sutures were not recognisable in the inner shell of any Phractopeltida.

The outer lattice-shell of the Phractopeltida, or their "cortical shell," is at least twice as broad, commonly about three times as broad, as the enclosed inner shell; it is much more varied in composition than the latter. Like the greater part of the Dorataspida we may distinguish here in the lattice-work two kinds of pores—parmal pores and sutural pores. The parmal pores are produced by the union of the meeting branches of the apophyses of each single spine, and are therefore visible on each isolated spine; whilst the sutural pores are formed by the meeting branches of the apophyses of neighbouring spines. The distinction of the parmal and the sutural pores, easy in most Dorataspida, is difficult in most Phractopeltida, because the sutures between the meeting branches are usually very early obliterated. However, the place of the obliterated suture is often indicated by the thickened condyles of the apophyses on both sides of the suture. Commonly also the form of the sutural pores is much more irregular than that of the parmal pores; the former are more or less constricted in the middle by the intumescence of the sutural condyles, whilst the latter are more roundish, elliptical, kidney-shaped, or square. The number of the pores in the outer shell in the typical normal form of Phractopeltida seems to be the same as in the most species of Dorataspis, Diporaspis, &c., between ninety and one hundred, viz., forty parmal pores and from fifty to sixty sutural pores. However, in many species this number is increased. Since in all Phractopeltida, each of the twenty plates is composed only of the meeting branches of two opposite apophyses, we find originally in each plate only two primary parmal pores or "aspinal pores." But in some species there occur four, six, or more pores in each plate; in this case two of them only are aspinal pores, all the others being "coronal pores." Moreover, in those species which exhibit on the base of each spine in the outer shell four crossed pores (Pl. , fig. 2), there are not four equivalent aspinal pores (as in the Tessaraspida), but the two opposite are primary or aspinal pores and the other two (different from them in size and form) coronal pores. However, the number of coronal pores in the Phractopeltida is never so large as in many Dorataspida, and the same holds good also for the increasing number of the irregular sutural pores. In none of the species observed does the total number of the pores in the outer shell reach two hundred.

The original mode of development of the apophyses composing the outer shell seems to be imitated by the free apophyses of the third order, which are developed from the radial spines outside the outer shell in all Phractopeltida, with the single exception of the simple ancestral genus Phractopelta. These apophyses of the third rank are also originally constantly two, opposite to one another (after the type of Lithophyllium, Dorataspis, &c.). Commonly they do not remain simple, but become branched, and by communication of the neighbouring branches small lattice-plates arise. Originally each of these free lattice-plates has only two parmal pores, but the number of the parmal pores increases afterwards, so that we may distinguish two (primary) aspinal pores, and two, four, or more (secondary) coronal pores. In the majority of species the two opposite apophyses are first crossed at right angles by a transverse beam, and the two parallel transverse beams are again crossed by perpendicular tertiary branches (again parallel to the apophyses). In this case the network of the free lattice-plates becomes more or less rectangular. But in other species the ramification of the apophyses assumes more the form of bifurcation or of irregular branching. As already said, the neighbouring free lattice-plates of this third order never meet, and therefore a complete third shell is never formed.

The different genera of Phractopeltida exhibit very remarkable differences in the development of free apophyses (or lattice-plates of the third order). Whilst in the numerous species of the ancestral genus Phractopelta all twenty spines remain simple, without such apophyses, only in a single observed species (representing the genus Pantopelta) were all twenty spines protected by them. In the three other genera only one part of the spines bears free apophyses, but not the other part. The most frequent form is Dorypelta (Pl. , fig. 2); here eight spines are simple (four equatorial and four polar spines of the hydrotomical plane), whilst twelve spines bear apophyses (eight tropical and four polar spines of the geotomical plane). In Octopelta the eight tropical spines only bear apophyses, whilst the twelve other (four equatorial and eight polar) are simple. In Stauropelta finally the four equatorial spines only are simple, whilst the sixteen other bear free apophyses (eight tropical and eight polar spines).

The Central Capsule of the Phractopeltida is constantly spherical, and enclosed between the two concentric spherical shells; it is therefore larger than the inner and smaller than the outer shell. Its wall is pierced by the twenty radial beams connecting the two shells. The shape of the central capsule and of the enveloping calymma is the same as in the other Acanthophracta and specially in the Dorataspida.

Synopsis of the Genera of Phractopeltida.

All twenty spines of the same form, All twenty spines without apophyses in the free external part, 366. Phractopelta.

All twenty spines with apophyses in the free part, 367. Pantopelta.

Twenty radial spines, partly without, partly with apophyses in the free external part, Eight tropical spines with apophyses, twelve others (eight polar and four equatorial) simple, 368. Octopelta.

Twelve radial spines (eight tropical and four polar) with apophyses, eight others (four polar and four equatorial) simple, 369. Dorypelta.

Sixteen radial spines (eight tropical and eight polar) with apophyses, four equatorial, simple, 370. Stauropelta.

All twenty spines of the same form,

All twenty spines without apophyses in the free external part,

366. Phractopelta.

All twenty spines with apophyses in the free part,

367. Pantopelta.

Twenty radial spines, partly without, partly with apophyses in the free external part,

Eight tropical spines with apophyses, twelve others (eight polar and four equatorial) simple,

368. Octopelta.

Twelve radial spines (eight tropical and four polar) with apophyses, eight others (four polar and four equatorial) simple,

369. Dorypelta.

Sixteen radial spines (eight tropical and eight polar) with apophyses, four equatorial, simple,

370. Stauropelta.

Genus 366. Phractopelta, Haeckel, 1881, Prodromus, p. 468.

Definition.—Phractopeltida with twenty simple radial spines, bearing no free apophyses outside the outer shell.

The genus Phractopelta is the most simple form among the Phractopeltida, and may be regarded as the common ancestral form of this family. All twenty spines are of nearly equal form and size, and bear no free apophyses on their free part, outside the two concentric shells. Phractopelta may be derived from Orophaspis by further development of the free apophyses, which by union of their branches form a second outer shell around the primary shell of that Dorataspid.

Subgenus 1. Phractopeltaris, Haeckel.

Definition.—Outer shell composed of twenty separated plates, the sutures of their meeting condyles not being grown together.

1. Phractopelta dorataspis, n. sp. (Pl. , fig. 1).

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with two elliptical aspinal pores, which are two to three times as broad as the irregular sutural pores. Radial spines (in the outer free part) compressed, linear, twice as long as the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.11, of the inner 0.05.

Habitat.—North Pacific (off Japan), Station 239, surface.

2. Phractopelta dyadopora, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with two kidney-shaped aspinal pores, which are three to four times as broad as the irregular sutural pores. Radial spines conical, about as long as the radius of the shell.

Dimensions.—Diameter of the outer shell 0.08, of the inner 0.04.

Habitat.—North Pacific, Station 256, surface.

3. Phractopelta diporaspis, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with two quadrangular aspinal pores, which are four to five times as broad as the irregular sutural pores. Radial spines compressed, sword-shaped, about as long as the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.04.

Habitat.—South Atlantic, Station 332, surface.

4. Phractopelta tessaraspis, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with four crossed, quadrangular, aspinal pores, the two opposite of which are much larger than the two others. Sutural pores small, roundish. Radial spines compressed, linear, about twice as long as the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.084, of the inner 0.032.

Habitat.—North Pacific (off Japan), Station 238, surface.

5. Phractopelta tetradopora, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with four crossed quadrangular (or nearly circular) aspinal pores, all of nearly the same size. Sutural pores polygonal or roundish. Radial spines cylindrical, two to three times as long as the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.11, of the inner 0.045.

Habitat.—North Pacific, Station 253, surface.

6. Phractopelta hexadopora, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with six aspinal pores, the two opposite of which are much larger than the four others. Sutural pores small, roundish. Radial spines compressed, two-edged, larger than the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—Central Pacific, Station 272, surface.

7. Phractopelta octadopora, n. sp.

Outer shell composed of twenty plates, the meeting condyles of which are separated by permanent sutures. Each plate commonly with eight aspinal pores, the four crossed being larger than the four others alternating with them. Sutural pores irregular. Radial spines conical, shorter than the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.12, of the inner 0.04.

Habitat.—Indian Ocean (Cocos Islands, surface), Rabbe.

Subgenus 2. Phractopeltidium, Haeckel.

Definition.—Outer shell composed of twenty united plates, the sutures of their meeting condyles being grown together.

8. Phractopelta aspidomma, n. sp.

Outer shell composed of twenty united plates, the meeting condyles of which are grown together. On the base of each radial spine (where its outer free part arises from the surface of the outer shell), two large elliptical aspinal pores, two to four times as large as the other roundish pores. Radial spines compressed, sword-shaped, about as long as the radius of the shell.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.05.

Habitat.—Equatorial Atlantic, Station 347, surface.

9. Phractopelta haliomma, n. sp.

Outer shell composed of twenty united plates, the meeting condyles of which are grown together. On the base of each radial spine two large kidney-shaped aspinal pores, little larger than the other irregular pores. Radial spines compressed, linear, two-edged, much longer than the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.03.

Habitat.—South Pacific, Station 295, surface.

10. Phractopelta tessaromma, Haeckel.

Outer shell composed of twenty united plates, the meeting condyles of which are grown together. On the base of each radial spine four crossed egg-shaped aspinal pores, two opposite of which are much larger than the two others. Sutural pores irregular. Radial spines cylindrical or little compressed, thin, longer than the diameter of the shell.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—Central Pacific, Station 266, surface.

11. Phractopelta hystrix, Haeckel.

Haliomma hystrix, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 37, Taf. v. figs. 1, 2.

Aspidomma hystrix, Haeckel, 1862, Monogr. d. Radiol., p. 424.

Outer shell composed of twenty united plates, the meeting condyles of which are grown together. On the base of each radial spine four crossed circular aspinal spines of equal size. Sutural pores roundish, of about the same size. Radial spines conical, about as long as the radius of the shell.

Dimensions.—Diameter of the outer shell 0.07, of the inner 0.024.

Habitat.—Mediterranean (Nice), J. Müller, surface.

Genus 367. Pantopelta, n. gen.

Definition.—Phractopeltida with twenty radial spines, each of which is protected by two free external apophyses.

The genus Pantopelta differs from all other Phractopeltida in the development of free protecting apophyses on all twenty radial spines. Only a single specimen of this rare form was seen, and in this all twenty spines exhibited no marked differences in form and size, but were more or less irregularly developed.

1. Pantopelta icosaspis, n. sp. (Pl. , fig. 4).

Apophyses of all twenty radial spines with forked anastomosing branches, forming a more or less irregular cup-like fenestrated shield, pierced by a variable number of pores. Distance of the apophyses from the outer shell equal to half its radius. Pores of the outer shell irregular, roundish, four to six times as broad as those of the inner shell. Radial spines compressed, sword-shaped, longer than the radius of the shell.

Dimensions.—Diameter of the outer shell 0.08, of the inner 0.03.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 368. Octopelta, n. gen.

Definition.—Phractopeltida with twelve simple spines (four equatorial and eight polar), and with eight tropical spines protected by external free apophyses.

The genus Octopelta differs from the other Phractopeltida in the possession of eight shields or pairs of free apophyses outside the outer lattice-shell; the spines bearing these apophyses are the eight tropical spines. The twelve other spines (eight polar and four equatorial) are quite simple, without apophyses.

1. Octopelta cultella, n. sp.

Apophyses of the eight tropical spines simple, compressed, knife-shaped, about as long as their distance from the outer shell. On the base of each spine (in the network of the outer shell) two orthogonal aspinal pores, two to three times as long as the other polygonal pores.

Dimensions.—Diameter of the outer shell 0.08, of the inner 0.03.

Habitat.—Tropical Atlantic, Station 338, surface.

2. Octopelta furcella, n. sp.

Apophyses of the eight tropical spines forked, each with two parallel simple fork-branches, about as long as their distance from the outer shell. On the base of each spine (in the outer shell) two kidney-shaped aspinal pores, about twice as broad as the other irregular pores.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—South Atlantic (off Tristan d'Acunha), Station 332, surface.

3. Octopelta scutella, n. sp. (Pl. , fig. 5).

Apophyses of the eight tropical spines crossed by a transverse beam, which is again crossed by two perpendicular branches; by union of these branches each tropical spine forms a square shield with four crossed pores and twelve to sixteen marginal spikes. On the base of each spine (in the surface of the outer shell) four crossed aspinal pores which correspond to those of the free shields; these are somewhat larger than the other pores.

Dimensions.—Diameter of the outer shell 0.12, of the inner 0.06.

Habitat.—Tropical Atlantic, Station 348, surface.

Genus 369. Dorypelta, Haeckel, Prodromus, p. 369.

Definition.—Phractopeltida with eight simple spines (four equatorial and four hydrotomical polar spines) and with twelve spines protected by external free apophyses (eight tropical and four geotomical polar spines).

The genus Dorypelta, the most common of all Phractopeltida which are protected by free apophyses, exhibits a very peculiar differentiation of its twenty radial spines. There are constantly eight simple spines and twelve spines with apophyses. The eight simple spines are the four equatorial spines and four polar spines placed in the hydrotomical median plane. The four other polar spines (placed in the geotomical meridian plane) and the eight tropical spines are protected by two opposite apophyses, which are now simple, now branched or shield-shaped. A similar differentiation occurs in no other Acanthophractida.

Subgenus 1. Dorypeltarium, Haeckel.

Definition.—Free apophyses of the radial spines simple, not branched.

1. Dorypelta stauroptera, n. sp.

Apophyses of the long compressed radial spines simple, conical, about as long as their distance from the shell. At the base of each spine (in the outer shell) two elliptical aspinal pores, two to three times as large as the other pores.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.044.

Habitat.—North Pacific, Station 238, surface.

2. Dorypelta gladiata, n. sp.

Apophyses of the long cylindrical radial spines simple, triangular, about half as long as their distance from the shell. At the base of each spine (in the outer shell) four crossed aspinal pores, the two opposite of which are much larger than the other two pores.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.04.

Habitat.—Central Pacific, Station 266, surface.

Subgenus 2. Dorypeltidium, Haeckel.

Definition.—Free apophyses of the radial spines branched, with free (not anastomosing) branches.

3. Dorypelta furcata, n. sp.

Apophyses of the long compressed spines simply forked, each with two simple parallel fork-branches. At the base of each spine two elliptical aspinal pores, much larger than the other roundish pores.

Dimensions.—Diameter of the outer shell 0.08, of the inner 0.04.

Habitat.—Central Pacific, Station 274, surface.

4. Dorypelta tetrodon, n. sp.

Apophyses of the long compressed spines crossed by a transverse beam, which bears four simple parallel fork-branches or spikes (perpendicular to the beam), two larger medial and two smaller lateral. At the base of each spine four crossed aspinal pores of nearly equal size, little different from the other pores.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.035.

Habitat.—South Pacific, Station 284, surface.

5. Dorypelta ramosa, n. sp.

Apophyses of the long cylindrical spines crossed by a transverse beam, which bears four to six irregularly branched spikes or fork-branches, the medial of which are larger than the lateral. At the base of each spine four crossed aspinal pores, two opposite of which are much larger than the two other pores.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.04.

Habitat.—South Pacific, Station 302, surface.

Subgenus 3. Dorypeltonium, Haeckel.

Definition.—Free apophyses of the radial spines branched, and forming perforated shields by union of their anastomosing branches.

6. Dorypelta lithoptera, n. sp.

Apophyses of the long compressed radial spines with anastomosing branches; each spine bearing two free separated shields (each with two roundish aspinal pores). At the base of each spine (in the network of the outer shell) two elliptical aspinal pores, larger than the other pores.

Dimensions.—Diameter of the outer shell 0.09, of the inner 0.03.

Habitat.—North Pacific, Station 239, surface.

7. Dorypelta tessaraspis, n. sp. (Pl. , fig. 2).

Apophyses of the long cylindrical spines with anastomosing branches; each spine bearing a single free shield with four crossed aspinal pores of equal size (on the margin of the shield twelve to sixteen spikes). At the base of each spine (in the outer shell) four crossed aspinal pores, about as large as the other roundish pores.

Dimensions.—Diameter of the outer shell 0.11, of the inner 0.05.

Habitat.—Central Pacific, Station 263, surface.

8. Dorypelta dodecaspis, n. sp.

Apophyses of the long two-edged spines with anastomosing branches; each spine bearing a single free shield with six to eight parmal pores (four crossed aspinal pores alternating with four outer coronal pores), on the margin of each shield twelve to sixteen spikes. At the base of each spine (in the outer shell) four crossed aspinal pores, about as large as the other irregular pores.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—North Pacific (off Japan), Station 235, surface.

Genus 370. Stauropelta, Haeckel, 1881, Prodromus, p. 468.

Definition.—Phractopeltida with four simple equatorial spines and sixteen spines protected by external free apophyses (eight tropical and eight polar spines).

The genus Stauropelta is distinguished from the other Phractopeltida by the possession of sixteen pairs of free apophyses (on the eight tropical and the eight polar spines); only the other four equatorial spines remain simple, without apophyses, and form a simple cross in the equatorial plane.

1. Stauropelta cruciata, n. sp. (Pl. , fig. 3).

Apophyses of the long polar and tropical spines crossed by a transverse beam, which is again crossed by two perpendicular branches parallel to the apophyses; branches with free ends, not united by concrescence. At the base of each spine (in the outer shell) two large elliptical aspinal pores, larger than the other irregular pores. Four equatorial spines simple, without apophyses, of the same size as the other sixteen spines.

Dimensions.—Diameter of the outer shell 0.12, of the inner 0.05.

Habitat.—Indian Ocean (Madagascar), Rabbe, surface.

2. Stauropelta stauropora, n. sp.

Apophyses of the long polar and tropical spines crossed by a transverse beam, which is again crossed by two perpendicular branches parallel to the apophyses; these branches are united by concrescence, and form a square shield with four crossed pores, the centre of which is pierced by the spine. At the base of each spine (in the outer shell) four crossed aspinal pores, corresponding to those of the shield, of about the same size as the other roundish pores. Four equatorial spines, simple, without apophyses, somewhat larger than the other sixteen spines.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—Indian Ocean, Sunda-Archipelago, Singapore, Trebing, surface.