Subfamily 1. Archidiscida, Haeckel

Definition.—Porodiscida with a simple spherical or lenticular latticed central chamber, surrounded by a single concentric latticed ring, which is divided by radial beams into two to six or more radial chambers.

Genus 212. Archidiscus, n. gen.

Definition.—Porodiscida with a simple central chamber, surrounded by a single concentric ring, which is divided by radial beams into two to six or more radial chambers, without radial spines on the margin.

The genus Archidiscus begins the long and polymorphous series of the Cyclodiscaria or of those Discoidea which do not possess the peculiar "phacoid shell" characteristic of the three preceding families, united as "Phacodiscaria." As already mentioned above, both these groups are probably of independent origin, derived from the Sphæroidea in different ways (compare pp. , , &c.). Among all Cyclodiscaria Archidiscus is the most simple, and probably the common ancestral form, from which the other genera may be derived.

Subgenus 1. Dioniscus, Haeckel.

Definition.—Ring with two chambers, separated by two radial beams.

1. Archidiscus dioniscus, n. sp.

Ring circular, connected with the central chamber by two radial beams, opposite in one axis, therefore two equal semicircular ring chambers. (This primitive form has an interesting reference to Saturnalis, Pl. , fig. 16, and differs from it only in the lattice-work covering both faces of the lenticular disk, the margin of which forms the ring.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Archidiscus dithalamus, n. sp.

Ring roundish, connected with the central chamber by two radial beams, not opposite in one axis; both semicircular ring chambers more or less unequal, one of them larger than the other, and sometimes much more prominent. (If this prominence increase, we can regard it as the beginning of spiral convolutions, Discospira.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.014.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 2. Trioniscus, Haeckel.

Definition.—Ring with three chambers, separated by three radial beams.

3. Archidiscus trioniscus, n. sp.

Ring triangular, roundish, equilateral, connected with the central chamber by three radial beams at equal distances (120°); therefore three equal ring chambers. (Resembles the central part of the disk of Tripodictya trigonaria, Pl. , fig. 8, and may be the ancestral form of it.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

4. Archidiscus trithalamus, n. sp.

Ring irregular, roundish, connected with the central chamber by three radial beams at unequal distances; therefore three ring chambers of different size. (If these differences be important, they introduce a spiral convolution in the further development of the Porodiscus arising from it.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.016.

Habitat.—South Pacific, Station 288, surface.

Subgenus 3. Tetroniscus, Haeckel.

Definition.—Ring with four chambers, separated by four radial beams.

5. Archidiscus stauroniscus, n. sp. (Pl. , figs. 9, 9a).

Ring regular, square, connected with the central chamber by four radial beams at equal distances, opposite in pairs in two axes perpendicular one to another; therefore four equal ring chambers (or congruent quadrants of the ring). Resembles the central part of the disk of Staurodictya medusa, &c. (Pl. , figs. 1-3); also of Staurodictya gracilis, Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3).

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

6. Archidiscus tetroniscus, n. sp.

Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not perpendicular one to another; therefore four ring chambers in pairs different, two opposite equal and larger than the two others.

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.016.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

7. Archidiscus tetrathalamus, n. sp.

Ring irregular, quadrangular, connected with the central chamber by four radial beams of increasing unequal length; therefore all four ring chambers of different size, gradually increasing in the following quadrants of the ring. Important as an ancestral type of such spiral and semi-spiral forms as Staurodictya cruciata (Pl. , figs. 4, 12, &c.) and Stylodictya clavata, Stylodictya stellata, &c., of Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. figs. 2, 7, 8, 9).

Dimensions.—Diameter of the ring 0.05 to 0.08, of the central chamber 0.06.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 4. Pentoniscus, Haeckel.

Definition.—Ring with five chambers, separated by five radial beams.

8. Archidiscus pentoniscus, n. sp.

Ring pentagonal or nearly circular, regular, connected with the central chamber by five radial beams of equal length and at equal distances (72°); therefore all five chambers of the ring of equal size and similar form. (Resembles the central part of the disk of Pentinastrum asteriscus, Pl. , fig. 2.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, surface.

Subgenus 5. Hexoniscus, Haeckel.

Definition.—Ring with six chambers, separated by six radial beams.

9. Archidiscus hexoniscus, n. sp. (Pl. , figs. 10, 10a).

Ring regular, hexagonal, or nearly circular, connected with the central chamber by six radial beams of equal length and at equal distances (60°); therefore all six chambers of the same size and form. (Resembles the central part of the disk of Hexinastrum geryonidum, Pl. , fig. 4.)

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

10. Archidiscus pyloniscus, n. sp. (Pl. , figs. 11, 11a).

Ring triangular, connected with the central chamber by six radial beams at alternating distances; therefore three larger chambers (of looser network) alternate with three smaller chambers (of denser network); pores of the former twice to three times as large as those of the latter. This species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these three larger ring chambers lose their few lattice-beams and so became open gates, we get Triolene or Triopyle, the original forms of the Pylodiscida.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

11. Archidiscus hexathalamus, n. sp.

Ring irregular, roundish, or hexagonal, connected with the central chamber by six radial beams of unequal increasing length; therefore all six ring chambers of gradually increasing size (beginning a spiral convolution, original form of some Discospira).

Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.014.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Subgenus 6. Circoniscus, Haeckel.

Definition.—Ring with seven or more chambers, separated by seven or more radial beams.

12. Archidiscus octoniscus, n. sp.

Ring circular or regular octagonal, connected with the central chamber by eight equidistant radial beams; therefore eight ring chambers of equal size. (Compare the central part of the disk of Porodiscus quadrigatus, Pl. , fig. 3.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

13. Archidiscus polythalamus, n. sp.

Ring circular, connected with the central chamber by nine to ten or more radial beams at nearly equal distances. Ring chambers nine to ten, more or less equal, sometimes also eleven to twelve, more different. (This species is very variable, and may perhaps be divided into a number of different "transformistic species.")

Dimensions.—Diameter of the ring 0.04 to 0.06, of the central chamber 0.015.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2925 fathoms.

Genus 213. Axodiscus, n. sp.

Definition.—Porodiscida with a simple central chamber, surrounded by one single concentric ring, which is divided by radial beams into two to six or more radial chambers; margin of the disk armed with radial spines.

The genus Axodiscus differs from the preceding Archidiscus only in the shape of the margin of the small lenticular disk, which is armed with a variable number of radial spines, indicating certain axes or radii of the shell. If these marginal spines at certain equal distances from the margin branch and their distal ends become united by these branches forming a concentric second ring, the genus passes into Porodiscus. The different number and disposition of the marginal spines are probably very important, as determining the later development of two to four or more radii in the different genera of Porodiscida.

1. Axodiscus stylophorus, n. sp.

Ring circular, with two equal semicircular chambers, connected with the central chamber by two opposite radial beams, which are prolonged outside into two strong conical spines.

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Axodiscus triradiatus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by three equidistant radial beams, which are prolonged outside into three short conical spines. (Differs from Archidiscus trioniscus in the possession of marginal spines.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

3. Axodiscus staurophorus, n. sp.

Ring regular, square, connected with the central chamber by four radial beams, which lie opposite in pairs in two perpendicularly crossed axes, and are prolonged outside into four delicate cylindrical spines.

Dimensions.—Diameter of the ring 0.045, of the central chamber 0.015.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Axodiscus hexagonus, n. sp.

Ring regular, hexagonal, connected with the central chamber by six radial beams at equal distances, which are prolonged outside into six strong pyramidal spines.

Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Axodiscus trigonus, n. sp.

Ring regular, triangular, equilateral, connected with the central chamber by six radial beams of alternating length and distance; therefore three smaller (perradial) chambers (with denser and darker network) alternating with three larger (interradial) chambers (with looser and finer network). On the margin three strong conical radial spines, arising in the radius of the larger chambers. (Differs from Archidiscus pyloniscus, Pl. , fig. 11, mainly in the strong angular spines on the three corners of the triangular shell.)

Dimensions.—Diameter of the ring 0.05, of the central chamber 0.014.

Habitat.—South Pacific, Station 296, depth 1825 fathoms.

6. Axodiscus octogonus, n. sp.

Ring circular or nearly octagonal, connected with the central chamber by eight radial beams at nearly equal distances, which are prolonged outside into eight short conical spines. (Differs from Archidiscus octoniscus in the marginal prolongation of the eight beams.)

Dimensions.—Diameter of the ring 0.04, of the central chamber 0.013.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

7. Axodiscus spinosus, n. sp.

Ring circular, connected with the central chamber by ten to twelve radial beams at nearly equal distances, which are prolonged outside into short conical spines of variable length. (May be regarded as an aculeate variety of Archidiscus polythalamus.)

Dimensions.—Diameter of the ring 0.04 to 0.05, of the central chamber 0.014.

Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2950 fathoms.