Page:Scientific results HMS Challenger vol 18 part 2.djvu/429

Rh

Definition.— (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is more or less constricted, either truncate or with a ring-like peristome. Cephalis rounded, without horn.

The genus Dictyocephalus has originated probably from Sethocorys by reduction and loss of the apical horn. The mouth is more or less constricted, either simple, truncate (Dictyocryphalus), or provided with a prominent, broad, hyaline, annular peristome (Dictyoprora).

Definition.—Mouth of the thorax constricted, with a prominent, ring-like or tubular, hyaline peristome.

1. Dictyocephalus amphora, n. sp. (Pl. 62, fig. 4).

Shell smooth, thick-walled, subovate, with slight collar stricture. Length of the two joints = 5 : 9, breadth = 6 : 8. Cephalis large, obtusely conical, with numerous oblique pore-canals. Thorax inflate, with six to eight transverse rows of roundish pores, increasing in size towards the base. Mouth constricted, one-third as broad as the thorax, with an internal diaphragm and a narrow hyaline peristome.

Dimensions.—Cephalis 0.05 long, 0.06 broad; thorax 0.09 long, 0.08 broad.

Habitat.—Central Pacific, Stations 265 to 272, depth 2425 to 2925 fathoms.

2. Dictyocephalus urceolus, n. sp.

? Eucyrtidium Mongolfieri, Bury, 1862, Polycystins of Barbados, pl. v. fig. 2.

Shell smooth, thick-walled, urceolate, with obliterated collar stricture. Length of the two joints = 5 : 12, breadth = 4 : 10. Cephalis campanulate, with numerous oblique pore-canals. Thorax inflate, with five or six transverse rows of roundish pores of equal size. Mouth constricted, nearly half as broad as the thorax, with a broad hyaline peristome.

Dimensions.—Cephalis 0.05 long, 0.04 broad; thorax 0.12 long, 0.1 broad.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.