Subfamily 1. Spongophacida, Haeckel, 1881, Prodromus, p. 461

Definition.—Spongodiscida with a simple circular disk, without radial appendages on the margin (neither solid spines nor chambered arms).

Genus 253. Spongodiscus, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

Definition.—Spongodiscida with a simple circular disk, without radial appendages and without an equatorial girdle on the margin.

The genus Spongodiscus represents the most simple and primitive form of the Spongodiscida, or of those Discoidea in which the central disk is more or less spongy, composed of an irregular fine framework. In my Monograph (1862, pp. 452, 460, 469) I had separated the true Spongodiscus (first described by Ehrenberg, loc. cit.) and the Spongocyclia; the former being characterised by the irregular spongy framework of the whole disk, whilst in the latter this framework includes in the central part some concentric circular rings (approaching Porodiscus). In the same way afterwards Stöhr (1880, loc. cit.) separated the genus Spongospira as spongy disks, which include in the central part some spiral convolutions. But as these differences are rather inconstant and not sharply discernible, I think it now better to regard these three forms as subgenera of Spongodiscus. All three have the common simple circular disk, without any marginal appendages.

Subgenus 1. Spongodisculus, Haeckel.

Definition.—Spongy framework of the disk quite irregular, without concentric rings or spiral convolutions.

1. Spongodiscus mediterraneus, Haeckel.

Spongodiscus mediterraneus, Haeckel, 1862, Monogr. d. Radiol., p. 461, Taf. xii. figs. 14, 15.

Spongy disk plain on both sides, with quite an irregular framework, without concentric rings and without radial piercing beams. Texture everywhere uniform; meshes eight to ten times as broad as the bars.

Dimensions.—Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to 0.008.

Habitat.—Mediterranean (Messina), Haeckel; also fossil in the Tertiary rocks of Sicily (Grotte), Stöhr.

2. Spongodiscus radiatus, n. sp.

Spongy disk plain on both sides, with quite irregular framework, without concentric rings, but with numerous piercing radial beams which are not prolonged into marginal spines. Texture everywhere uniform; meshes once and a half to twice as broad as the bars.

Dimensions.—Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to 0.003.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Spongodiscus resurgens, Ehrenberg.

Spongodiscus resurgens, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B. iv., fig. 16.

Spongodiscus resurgens, Stöhr, 1880, Palæontogr., xxvi. p. 117, Taf. vi. fig. 11.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the thin periphery, with an irregular framework, without concentric rings, but with numerous piercing radial beams. Texture equal; meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in the Tertiary rocks of Sicily and Barbados.

4. Spongodiscus favus, Ehrenberg.

Spongodiscus favus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the periphery, with an irregular framework, without concentric rings. Texture different, in the outer half with numerous radial beams and loose network, the meshes of which are three to four times as large as in the darker and denser framework of the centre.

Dimensions.—Diameter of the disk 0.2, of the outer meshes 0.008 to 0.012, of the inner meshes 0.002 to 0.003.

Habitat.—North Atlantic, Greenland, Færöe Channel (John Murray), surface.

5. Spongodiscus biconcavus, n. sp.

Spongy disk biconcave, in the peripheral, ring-like, thickened part twice as thick as in the hollowed central part, with an irregular framework, without concentric rings. Texture different, in the outer half looser than in the inner, darker part; meshes of the outer part five to six times, of the inner twice to three times, as broad as the bars.

Dimensions.—Diameter of the disk 0.25, of the outer meshes 0.01 to 0.012, of the inner 0.004 to 0.006.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Spongocyclia, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Definition.—Spongy framework of the disk in the inner part with concentric, circular rings, in the outer part irregular.

6. Spongodiscus cycloides, Haeckel.

Spongodiscus cycloides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Spongocyclia cycloides, Haeckel, 1862, Monogr. d. Radiol., p. 469, Taf. xxviii. fig. 1.

Spongy disk on both sides plain, in the central part with five to ten concentric, circular rings, in the peripheral part quite irregularly and densely spongy. Meshes twice to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to 0.006.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands).

7. Spongodiscus spongocyclia, Haeckel.

Spongocyclia triangularis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 119, Taf. vii. fig. 5.

Spongy disk lenticular, in the thicker central part with eleven to twelve circular, concentric rings, in the thinner, peripheral zone irregularly spongy. Meshes twice to four times as broad as the bars. (The triangular form in the specimen figured by Stöhr is accidental, produced by the broken margin.)

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Barbados (Haeckel) and Sicily (Stöhr).

Subgenus 3. Spongospira, Stöhr, 1880, Palæontogr., vol xxvi. p. 120.

Definition.—Spongy framework of the disk in the inner part with spiral convolutions, in the outer part irregular.

8. Spongodiscus florealis, Haeckel.

Spongospira florealis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 120, Taf. vii. fig. 6.

Spongy disk lenticular, in the thicker central part with five to six spiral convolutions, in the outer peripheral zone irregularly spongy. No radial beams piercing the framework. Meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.26, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Sicily (Grotte), Stöhr.

9. Spongodiscus spiralis, n. sp.

Spongospira spiralis, Haeckel, 1881, Prodromus.

Spongy disk on both sides plain, with twelve to sixteen spiral convolutions in the central part, with irregular, spongy framework in the outer part, pierced by numerous interrupted radial beams. Meshes five to six times as broad as the bars.

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.01 to 0.012.

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

Genus 254. Spongophacus, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus Spongophacus, represented hitherto only by a single but interesting species, differs from Spongodiscus by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as Perichlamydium in the Porodiscida, and resembles also Periphæna, &c., in the Phacodiscida.

1. Spongophacus periphæna, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

Dimensions.—Diameter of the disk 0.2; breadth of the girdle 0.05.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.