Subfamily 2. Phractacanthida, Haeckel

Definition.—Astrolonchida with twenty radial spines, each of which bears two opposite apophyses or lateral transverse processes; sometimes two longitudinal rows of opposite apophyses.

Genus 326. Lithophyllium, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52.

Definition.—Astrolonchida with two simple, not branched, opposite apophyses on each radial spine.

The genus Lithophyllium was founded by J. Müller for a single species (Lithophyllium foliosum), which we also here retain as the type of the genus. It is the first observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The two opposite apophyses are here simple, whilst in the other genera of the subfamily they are branched or multiplied.

1. Lithophyllium cruciatum, Haeckel.

Acanthometra cruciata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf xi. fig. 11.

Xiphacantha cruciata, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf. xviii. fig. 13.

Spines cylindrical, very thin, crossed perpendicularly in the distal third by a thin transverse beam; both lateral rods of the cross have the same length as the distal end. Apex simple. Base pyramidal, without leaf-cross.

Dimensions.—Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.

Habitat.—Mediterranean, Atlantic, Stations 352 to 354, &c., surface.

2. Lithophyllium gladiatum, n. sp. (Pl. , fig. 3).

Spines compressed, sword-shaped, two-edged, crossed perpendicularly in the middle part by a broad, somewhat curved transverse beam; both lateral rods of the cross are triangular compressed, and have the same length as the proximal end. Apex simple. Base pyramidal, without leaf-cross.

Dimensions.—Length of the spines 0.2 to 0.25, breadth 0.01.

Habitat.—North Pacific, Station 241, surface.

3. Lithophyllium condylatum, n. sp.

Spines compressed quadrangular, tapering from the broader middle towards the two ends; from the middle part arise two opposite perpendicular apophyses, which bear on the rounded end a thickened condyle. Apex simple. Base pyramidal, with a small leaf-cross.

Dimensions.—Length of the spines 0.1 to 0.12, breadth in the middle part 0.02.

Habitat.—Central Pacific, Station 266 to 272, surface.

4. Lithophyllium foliosum, J. Müller.

Lithophyllium foliosum, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52, Taf. xi. figs. 6-10.

Xiphacantha foliosa, Haeckel, 1862, Monogr. d. Radiol., p. 385.

Spines lanceolate, tapering from the broader middle towards the two ends. From the middle part or from the outer third arise two opposite triangular apophyses, which are not perpendicular to the axis of the spine, but form an acute angle with its distal part. Therefore each spine represents a broad leaf with a middle rib and with three lobes or truncated teeth. The distal apex is distinguished by a violet colour. Base pyramidal, without leaf-cross. Central capsule yellow.

Dimensions.—Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.

Habitat.—Mediterranean, French shore, Saint Tropez, J. Müller.

Genus 327. Phractacantha, Haeckel, 1881, Prodromus, p. 465.

Definition.—Astrolonchida with two branched, but not latticed, opposite apophyses on each radial spine.

The genus Phractacantha differs from its ancestral form, the preceding Lithophyllium by the ramification of the apophyses, which are either forked or bear lateral branches. If the prolonged fork-branches of the neighbouring spines meet and form a lattice-shell, this genus passes over into Phractaspis, the common ancestral form of the Diporaspida.

1. Phractacantha bifurca, n. sp.

Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses; ends of the fork branches acute.

Dimensions.—Length of the spines 0.1, breadth 0.006.

Habitat.—Central Pacific, Station 274, surface.

2. Phractacantha bipennis, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle arise two opposite broad, forked apophyses; ends of the fork-branches broad and obtuse.

Dimensions.—Length of the spines 0.15, breadth in the middle 0.012.

Habitat.—Central Pacific, Station 266, surface.

Genus 328. Doracantha, Haeckel, 1881, Prodromus, p. 465.

Definition.—Astrolonchida with two latticed or fenestrated apophyses on each radial spine.

The genus Doracantha arises from the foregoing Phractacantha by union of the fork-branches of the apophyses on each spine. By this concrescence is formed a polygonal or roundish plate with two pores, pierced by the radial spine between them. Doracantha may be regarded as a Dorataspis, in which the twenty small fenestrated plates have not become united.

1. Doracantha dorataspis, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle part of each spine arise two opposite forked apophyses; the neighbouring fork-branches are recurved and united in the tangential plane; so that each spine bears a plate or shield with two elliptical pores; the margin of the roundish plate bears a variable number of short teeth.

Dimensions.—Length of the spines 0.2, breadth 0.02.

Habitat.—Central Pacific, Station 271, surface.

Genus 329. Astrolonche, Haeckel, 1881, Prodromus, p. 465.

Definition.—Astrolonchida with numerous simple apophyses (four to eight or more on each radial spine), which are arranged in two opposite longitudinal rows (rarely in six such rows, opposite in three parallel planes).

The genus Astrolonche differs from the preceding Phractacanthida in the multiplication of the simple apophyses. Commonly these are opposite in pairs in two longitudinal rows (on the two edges of the compressed spine, at least two on each side). But sometimes (in the subgenus Astrolonchidium) there are six instead of two longitudinal rows of teeth, and these are placed in three parallel planes.

Subgenus 1. Astroloncharium, Haeckel.

Definition.—Each spine with two longitudinal rows of apophyses, opposite in one meridian plane.

1. Astrolonche bicruciata, n. sp.

Spines compressed, two-edged, almost of equal breadth throughout their whole length, with simple apex and small leaf-cross at the base. From the two edges of the middle part of each spine arise two pairs of opposite apophyses, which are compressed and a little curved (convex on the distal, concave on the proximal margin). All four apophyses are of the same size and form; the radial distance of each pair much smaller than their common distance from the centre.

Dimensions.—Length of the spines 0.25, breadth 0.02.

Habitat.—Central Pacific, Station 270, surface.

2. Astrolonche mucronata, Haeckel.

Acanthometra mucronata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf. x. fig. 9.

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

Spines conical, little compressed, with simple apex and small leaf-cross at the base. From the basal half of each spine arise two pairs of opposite apophyses, which exhibit a very different form. The upper or distal apophyses (nearly in the middle of the spine) are flat, leaf-shaped, broadened in the periphery, often lobed, and sometimes branched or even fenestrated. (Transition to Phractaspis and Dorataspis, or to Phractopelta?) The lower or proximal apophyses are thick, simple, all slightly curved; they are equidistant from the former and from the centre.

Dimensions.—Length of the spines 0.2 to 0.3, greatest breadth 0.01.

Habitat.—Mediterranean (Cette on the French shore), surface, J. Müller.

3. Astrolonche pectinata, Haeckel.

Acanthometra pectinata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. x. figs. 1, 2.

Xiphacantha pectinata, Haeckel, 1862, Monogr. d. Radiol., p. 386.

Spines compressed quadrangular, with short, simple or bifid apex, pyramidal on the base, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; three to four slender teeth in each row.

Dimensions.—Length of the spines 0.2, breadth 0.08.

Habitat.—Mediterranean, Cette (French shore), surface, J. Müller.

4. Astrolonche pinnata, n. sp.

Spines in the distal half compressed, linear, two-edged, with bifid apex; in the proximal half three times as broad lanceolate, at the base pyramidal, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; four to six broad triangular teeth in each row.

Dimensions.—Length of the spines 0.3 to 0.4, breadth in the outer half 0.012, in the inner half 0.03 to 0.04.

Habitat.—South Atlantic, Station 332, surface.

Subgenus 2. Astrolonchidium, Haeckel.

Definition.—Each spine with three parallel double rows of opposite apophyses.

5. Astrolonche serrata, Haeckel.

Xiphacantha serrata, Haeckel, 1862, Monogr. d. Radiol., p. 386, Taf. xvii. fig. 3, Taf. xviii. figs. 14a, 14b.

Xiphacantha serrata, R. Hertwig, 1879, Organismus d. Radiol., p. 11, Taf. ii. fig. 4.

Acanthometra serrata, Haeckel, 1860, Monogr. d. Radiol., p. 807.

Spines in the distal half thin, nearly cylindrical or a little compressed, thinned towards the short simple or bifid apex; in the proximal half three to six times as broad, four-winged, with six longitudinal rows of opposite apophyses. From the edges of the two broader (lateral) wings arise three to four pairs of strong conical teeth; from the edges of the two smaller (sagittal) wings arise also three to four pairs of teeth, but very short and broad, triangular; each of these teeth bears on both its (lateral) sides two opposite slender conical teeth, which are parallel to the large conical teeth of the lateral wings. Therefore all teeth (eighteen to twenty-four) are placed opposite in pairs in three parallel planes. Base of the spines pyramidal, with a small leaf-cross. The central capsule of this large and very remarkable species commonly entirely includes the apophyses of the spines, and is opaque, whitish.

Dimensions.—Length of the spines 0.2 to 0.3, breadth of the distal half 0.002 to 0.004, of the proximal half 0.01 to 0.02.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.