The genus Pteroscenium differs from the preceding Archiscenium only in the ramification of the internal columella, and therefore exhibits to it the same relation that Cladoscenium bears to Euscenium. The branches of the columella form also here verticils of ascending branches, three in each verticil, and their distal ends are inserted on the inner surface of the lattice-shell.

1. Pteroscenium arcuatum, n. sp. (Pl. 98, fig. 4).

Shell campanulate, smooth, nearly conical, somewhat broader than long, with irregular dense network of small circular pores. Columella straight, with two or three triradiate verticils of horizontal lateral branches, which are inserted in the shell-wall. Horn slender pyramidal, as long as the shell. Three divergent feet twice as long as the horn, strongly curved, thorny, three-edged; the distance of their pointed ends twice as broad as the shell. From the outer edge of each foot arise numerous ascending bristles, which are connected together and with similar lateral branches of the horn by curved arches, forming three delicate spiny vertical wings.

Dimensions.—Shell 0.06 long, 0.08 broad.

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

2. Pteroscenium arcadophorum, n. sp.

Shell campanulate, smooth, with irregular polygonal pores, very similar to the preceding species but with much broader wings, forming several arcades with three to five rows of irregular meshes. Columella with five or six triradiate verticils of lateral branches. Horn twice as long as the shell, of the same length as the strongly curved spinulate feet.

Dimensions.—Shell 0.09 long, 0.11 broad.

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

3. Pteroscenium pinnatum, n. sp. (Pl. 53, figs. 14, 15, 16).

Shell campanulate, smooth, somewhat longer than broad, with irregular delicate network of small roundish pores. Columella straight, with numerous (eight to twelve) triradiate verticils of ascending lateral branches, which are inserted in the shell-wall. The uppermost end of the columella is a conical apical horn. The three divergent feet are smooth, slender, conical, slightly curved, about as long as the shell, pinnate, with six to ten pairs of ascending lateral branches, parallel to those of the columella and inserted on the three vaulted lateral wings. (Fig. 14 exhibits the outside of the shell, fig. 15 the internal structure of the cortina, fig. 16 the basal view.)

Dimensions.—Shell 0.1 long, 0.12 broad.

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

4. Pteroscenium spinulosum, n. sp.

Shell campanulate, spinulate, about as long as broad, with small and numerous irregular polygonal pores, very similar to the preceding species, but differing in the more slender form of the horn and the feet, bearing more numerous lateral branches (twelve to sixteen pairs on each foot). Columella with six to eight triradiate verticils. Horn about as long as the shell.

Dimensions.—Shell 0.1 long, 0.1 broad.

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

5. Pteroscenium macropodium, n. sp.

Shell campanulate, spinulate, with irregular polygonal pores; very similar to the two preceding species, but differing in the size and shape of the three feet, which are for the most part solid, triangular, nearly parallel, vertical, very slender, three times as long as the shell, latticed only at the curved base, with few pairs of lateral branches. Columella with four to six triradiate verticils, as long as the stout triangular pyramidal horn.

Dimensions.—Shell 0.1 long, 0.08 broad.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

6. Pteroscenium tripocolpum, n. sp.

Shell campanulate, spinulate, similar to Euscenium tricolpium (Pl. 53, fig. 12) with three vaulted hemispherical bosoms between the three delicate arachnoidal vertical wings. Network loose, very irregular, with polygonal meshes of very different sizes. Columella with three or four triradiate verticils, as long as the slender pyramidal horn. Three feet twice as long, somewhat curved, widely divergent, with three or four pairs of lateral branches. The three edges of the feet and of the horn are elegantly denticulated.

Dimensions.—Shell 0.06 long, 0.09 broad.

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

Genus 508. Peridium,^[125] Haeckel, 1881, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) without internal columella, with an apical horn.

The genus Peridium (or Archiperidium, Prodromus, loc. cit.) and the two following nearly allied genera form together the small group of Archibursida, differing from the four preceding genera (the Euscenida) in the absence of an internal free columella. The three basal feet have therefore no direct connection with the apical horn. Peridium, the ancestral form of the Archibursida, may have originated either from Euscenium by reduction and loss of the columella, or directly from Tripospyris by loss of the sagittal ring and the longitudinal constriction.

Subgenus 1. Peridarium, Haeckel.

Definition.—Feet smooth, simple, neither spiny nor branched.

1. Peridium lasanum, n. sp.

Shell subspherical, smooth, with subregular circular pores. Basal plate with three large meshes. Horn apical, vertical, of the same size and form as the three divergent smooth feet, slender pyramidal, twice to three times as long as the shell.

Dimensions.—Shell-diameter 0.06 to 0.07, length of the three spines 0.15 to 0.2.

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

2. Peridium papillatum, n. sp.

Shell subspherical, papillate, with subregular circular pores. Basal plate with four meshes (two major cardinal and two minor jugular pores). Horn occipital, oblique, three-sided pyramidal, half as long as the shell and as the three widely divergent, subhorizontal, smooth feet.

Dimensions.—Shell diameter 0.07 to 0.08, length of the horn 0.04, of the feet 0.08.

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

3. Peridium curvipes, n. sp.

Shell hemispherical, thorny, with irregular roundish pores. Basal plate with six pores (two larger middle cardinal, two smaller anterior jugular and two smaller posterior cervical pores, as in Pl. 53, figs. 13, 18). Horn conical, oblique, arising from the middle of the occipital face, half as long as the shell. Feet slender, conical, curved, smooth, twice as long as the shell.

Dimensions.—Shell 0.04 long, 0.06 broad; horn 0.02 long; feet 0.08 long.

Habitat.—Tropical Pacific, Station 206, depth 2100 fathoms.

Subgenus 2. Archiperidium, Haeckel.

Definition.—Feet spiny or branched.

4. Peridium spinipes, n. sp. (Pl. 53, fig. 9).

Shell ovate, rough or thorny, with irregular roundish pores. Basal plate with four pores (two larger cardinal and two smaller jugular pores). Horn oblique, occipital, three-sided pyramidal, half as long as the shell, connected with the caudal foot by a prominent crest. Three feet horizontally expanded, prismatic, spiny, about as long as the shell.

Dimensions.—Shell 0.08 long, 0.06 broad; horn 0.04 long, feet 0.06 to 0.09 long.

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

5. Peridium palmipes, n. sp. (Pl. 53, fig. 10).

Shell ovate, smooth, with irregular roundish pores. Basal plate with three large pores. Horn oblique, three-sided pyramidal, about as long as the shell, inserted near its occipital base. Three feet prismatic, slender, half as long, ending with a broad dentate plate.

Dimensions.—Shell 0.06 long, 0.05 broad; horn 0.05 long, feet 0.03 long.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

6. Peridium alatum, n. sp. (Pl. 97, fig. 7).

Shell subspherical smooth, with regular circular, hexagonally-framed pores. Basal plate with nine pores (three larger central and six smaller distal pores). Horn apical, of equal size and the same form as the three feet, three-sided prismatic, with three broad prominent wings, somewhat longer than the shell.

Dimensions.—Shell 0.07 long, 0.08 broad; horn and feet 0.1 to 0.12 long.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

7. Peridium cervinum, n. sp.

Shell subspherical, spiny, with subregular circular pores. Basal plate with four pores (?). Horn apical, conical, about as long as the shell. Feet three to four times as long, cylindrical curved, with irregular simple or forked branches like the antlers of a deer.

Dimensions.—Shell diameter 0.1, horn 0.1 long, feet 0.3 to 0.4 long.

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

Genus 509. Archipera,^[126] Haeckel, 1881, Prodromus, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) without internal columella, with two or more apical horns.

The genus Archipera differs from the preceding Peridium only in the multiplication of the apical horn, which in the latter is always simple. The number of horns is usually two or three, sometimes four or more. The species bearing three horns may be derived directly from Triceraspyris by loss of the sagittal ring.

1. Archipera cortiniscus, n. sp. (Pl. 98, fig. 5).

Shell ovate, thorny, with large roundish pores, which are closed by sieve-plates with numerous small porules. Basal plate with two pairs of simple large pores (two smaller jugular and two larger cardinal, similar to Pl. 98, fig. 10b). Two horns divergent, curved, slender, pyramidal; the apical horn longer than the shell, the frontal horn shorter. Three feet divergent, longer than the shell, three-sided prismatic, at the distal end club-shaped, thorny.

Dimensions.—Shell 0.1 long, 0.08 broad; horns and feet 0.11 to 0.14 long.

Habitat.—Tropical Pacific, Station 225, depth 4475 fathoms.

2. Archipera pentacantha, n. sp.

Shell pear-shaped, smooth, with numerous and small irregular roundish pores. Basal plate with three larger pores. Two horns and three feet of nearly equal size and similar form, three-sided prismatic, about as long as the shell diameter, somewhat curved. The apical horn stands on the apex, the frontal horn half-way up the shell.

Dimensions.—Shell 0.08 long, 0.06 broad; horns and feet 0.05 to 0.07 long.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Archipera bicornis, n. sp.

Shell ovate, rough, with small regular circular, sparsely scattered pores. Basal plate with four larger central and a peripheral coronal of twelve smaller pores. Two horns near the apex widely divergent, somewhat shorter than the shell, of equal size and similar form. Three feet twice as long, horizontally expanded. All five spines slender, three-sided pyramidal, straight.

Dimensions.—Shell 0.07 long, 0.06 broad; horns 0.05 long, feet 0.1 long.

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

4. Archipera tricornis, n. sp.

Shell subspherical, smooth, with subregular circular pores. Basal plate with four large meshes (two major cardinal and two minor jugular pores). On the apex three divergent pyramidal horns of different size, one larger occipital and two smaller frontal horns. Three feet prismatic, about twice as long as the shell.

Dimensions.—Shell diameter 0.05, length of the feet 0.1.

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

5. Archipera quadricornis, n. sp.

Shell ovate, smooth, with a small number of irregular roundish, widely scattered pores. Basal plate with four crossed meshes of nearly equal size. On the equator there arise four divergent prismatic horns of nearly equal size, three of which correspond to the three feet, whilst the fourth is opposite to the caudal foot. The three feet are also prismatic, as long as the shell, horizontally expanded. (Similar to the upper half of Lithomelissa decacantha, Pl. 56, fig. 2, but without thorax.)

Dimensions.—Shell 0.05 long, 0.04 broad; horns and feet 0.06 long.

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

6. Archipera multicornis, n. sp.

Shell hemispherical, spiny, with irregular polygonal pores. Basal plate with six meshes (?). Between the smaller spines of the surface arise six larger conical divergent horns. Three feet also conical, divergent, about twice as long as the shell and the horns.

Dimensions.—Shell 0.05 long, 0.07 broad; horns 0.05 long, feet 0.1 long.

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

Genus 510. Archibursa,^[127] Haeckel, 1881, Prodromus, p. 429.

Definition.—Archiperida (vel Monocyrtida triradiata clausa) without internal columella and without apical horn.

The genus Archibursa has probably arisen from Peridium by loss of the apical horn, and is the only genus of Archiperida which bears no horn. The three basal feet are well-developed. It differs from the similar Tristylospyris by the absence of the sagittal ring and the corresponding longitudinal constriction.

1. Archibursa tripodiscus, n. sp. (Pl. 98, fig. 6).

Shell subspherical, smooth, with irregular roundish pores. Basal plate with three large triangular pores of equal size (fig. 6). Three feet widely divergent, straight, three-sided prismatic, about as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.07, length of the feet 0.09.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Family LX. Phænocalpida, n. fam.

Definition.—Monocyrtida multiradiata. (Cyrtoidea with a simple, not jointed shell, resembling a simple cephalis, with numerous radial apophyses (four to nine or more).

The family Phænocalpida, composed of the Archiphormida and Archiphænida of my Prodromus, comprises those Cyrtoidea in which the lattice-shell is quite without transverse constriction, but bears numerous radial apophyses. The two subfamilies differ in the shape of the basal mouth, which in the Archiphormida is a simple wide opening, but is closed in the Archiphænida by a lattice-plate.

Several Phænocalpida were formerly described by Ehrenberg, viz., Halicalyptra virginica (in 1844) and Litharachnium arachnodiscus (in 1872, called by him Carpocanium, though it is quite different from this genus, and closely allied to my Litharachnium tentorium, figured in 1862). These forms belong to the Archiphormida (with open mouth). Several fossil Archiphænida (with closed mouth) were figured by Ehrenberg, in 1875, as belonging to Petalospyris (ocellata, carinata, flabellum), though the absence of the sagittal ring and the corresponding longitudinal constriction demonstrates their character as Phænocalpis.

The Phænocalpida are probably an artificial family, composed of three or four (or perhaps more) different groups, which have a quite different origin. The Litharachnida (genera 511-515) and the Haliphormida (genera 516-518) are probably derived from the Sethophormida by loss of the cephalis, the retrograde metamorphosis of which may be observed in all its different stages. The Halicalyptrida (genera 519-521) are perhaps independent of the other Phænocalpida, and may be Archicorida which have produced a corona of teeth around the mouth, without relation to lost radial ribs. The Phænoscenida (Phænocalpis, Phænoscenium) may be derived from the Euscenida (genera 504-507) by interpolation of interradial feet between the three primary ones, or directly from the Plectoidea. The Calpophænida, on the other hand (Calpophæna, Archiphæna), may have arisen from the Zygospyrida (Petalospyris, Gorgospyris) by loss of the sagittal ring and the longitudinal constriction. The phylogeny of the Phænocalpida is therefore a very complicated problem, as yet unsolved.

Synopsis of the Genera of Phænocalpida.

Subfamily 1. Archiphormida, Haeckel, 1881, Prodromus, p. 428.

Definition.—Phænocalpida with the basal mouth of the shell open (vel Monocyrtida multiradiata aperta).

Genus 511. Bathropyramis,^[128] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archiphormida (vel Monocyrtida multiradiata aperta) with simple, slender pyramidal shell and numerous radial beams (six to nine or more). Network simple, with large, unfenestrated, quadrangular meshes.

The genus Bathropyramis and the following four nearly allied genera form together a peculiar group of Archiphormida, the Litharachnida, possessing near relations to Sethopyramis and the allied Sethophormida, from which they are probably derived by reduction and loss of the small cephalis. The shell in all these forms is distinctly pyramidal, composed of numerous divergent radial beams (commonly six to nine), which form the edges of the pyramid, and are connected by parallel horizontal rings. The quadrangular meshes so produced are quite simple in Bathropyramis. This genus cannot be sharply separated from Sethopyramis, its ancestral form.

Subgenus 1. Acropyramis, Haeckel, 1881, Prodromus, p. 428.

Definition.—Shell smooth, without spines on the surface.

1. Bathropyramis acephala, n. sp.

Shell smooth, slenderly pyramidal, with three cortinar pores at the apex and with six stout radial beams or longitudinal ribs, connected by twelve to sixteen complete hexagonal horizontal rings. Meshes nearly square, increasing gradually in size towards the mouth.

Dimensions.—Shell 0.25 long, 0.15 broad.

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

2. Bathropyramis quadrata, n. sp. (Pl. 54, fig. 1).

Shell smooth, slenderly pyramidal, with three cortinar pores at the apex and nine stout radial beams, connected by eight to twelve complete circular horizontal rings. Meshes subregular, square, increasing in size gradually towards the circular mouth.

Dimensions.—Shell 0.2 to 0.3 long, 0.12 to 0.2 broad.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Bathropyramis trapezoides, n. sp. (Pl. 54, fig. 3).

Shell smooth, broadly pyramidal, with four cortinar pores at the apex and eight (or sometimes nine) stout radial beams, connected by twelve to sixteen complete octagonal horizontal rings. Meshes trapezoidal, of nearly equal length, but gradually increasing in breadth.

Dimensions.—Shell 0.3 long, 0.3 broad.

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

4. Bathropyramis interrupta, n. sp. (Pl. 55, fig. 7).

Shell smooth, flatly pyramidal, nearly discoidal, with four cortinar pores at the apex and nine to ten stout radial beams, connected by eight to sixteen interrupted rings; the rings are complete only in the apical part, in the distal part more or less irregularly interrupted.

Dimensions.—Shell 0.12 long, 0.36 broad.

Habitat.—North Atlantic, Station 354, surface.

5. Bathropyramis medusa, n. sp.

Shell smooth, flatly pyramidal, nearly discoidal, with four cortinar pores and numerous radial beams (thirty to fifty); the four perradial of these are prolongations of the four cortinar beams, and alternate with four interradial of the same size. Between these are intercalated eight adradial beams arising from the third ring; and between the former and the latter, sixteen to twenty-four peripheral radial beams, arising from the fourth to the sixth ring. The inner four to six rings are complete, the outer ten to fifteen irregularly interrupted.

Dimensions.—Shell 0.08 long, 0.3 to 0.4 broad.

Habitat.—South Atlantic, Station 338, surface.

Subgenus 2. Cladopyramis, Haeckel, 1881, Prodromus, p. 428.

Definition.—Shell spiny, with prominent simple or branched spines on the surface.

6. Bathropyramis spinosa, n. sp.

Shell spiny, slenderly pyramidal, with three cortinar pores at the apex and with nine strong radial beams, connected by fifteen to twenty complete parallel rings. Meshes subregular square, increasing gradually in size. Surface covered with simple, strong conical spines, arising from the nodal points.

Dimensions.—Shell 0.24 long, 0.16 broad.

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

7. Bathropyramis ramosa, n. sp. (Pl. 54, fig. 4).

Shell spiny, slenderly pyramidal, with three cortinar pores at the apex, and with nine (or sometimes eight or ten) strong radial beams, connected by fifteen to eighteen complete parallel rings. Meshes subregular, square, increasing gradually in size. Surface covered with forked or irregularly branched spines, arising from the nodal points.

Dimensions.—Shell 0.3 long, 0.17 broad.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Genus 512. Cinclopyramis,^[129] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archiphormida (vel Monocyrtida multiradiata aperta) with simple, slender, pyramidal shell, and numerous radial beams (six to nine or more). Network double, with a delicate arachnoidal fenestration, filling up the large quadrangular meshes.

The genus Cinclopyramis differs from the preceding Bathropyramis in the development of a very delicate secondary network, filling up the large quadrangular meshes, which are produced by the crossing of the radial beams and the parallel horizontal rings. It therefore bears the same relation to the preceding genus that Plectopyramis does to Sethopyramis; it is perhaps derived directly from the former by loss of the small cephalis.

1. Cinclopyramis cribellum, n. sp.