Page:Scientific results HMS Challenger vol 18 part 2.djvu/572

1448 The genus Stichopera, and the two following genera, represent the small subfamily of Stichoperida, or those triradiate Stichocyrtida in which the terminal mouth is closed by lattice-work. In Stichopera the three radial appendages are either solid lateral ribs or longitudinal combs of spines; the closed basal part of the shell is rounded, not pointed. It may be derived either from Stichopilium by closure of the mouth, or from Lithornithium by increase of the number of the joints.

Definition.—Shell with three solid radial ribs, or longitudinal dentate crests.

1. Stichopera ovata, n. sp.

Shell ovate, with three distinct strictures. Length of the four joints = 2 : 3 : 4 : 6. The fourth joint is the broadest, and twice as long as the second, with hemispherical basal pole. Cephalis hemispherical, with a conical horn of twice the length. Along the second and third joints descend three prominent divergent ribs, which disappear in the middle zone of the fourth joint. Pores regular, circular.

Dimensions.—Length of the shell (with four joints) 0.15, breadth 0.1. Length of the single joint, a 0.02, b 0.03, c 0.04, d 0.06.

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

2. Stichopera lagena, n. sp.

Shell bottle-shaped, with six sharp strictures; the upper half is slender, conical, and composed of six joints of nearly equal length, the lower half is formed only by the last subspherical joint. Cephalis subspherical, with a pyramidal horn of the same length. From its base arise three divergent ribs, which attain the greatest height in the fourth joint, and disappear in the sixth joint. (Similar to Stichophæna ritteriana, Pl. 75, fig. 12, but only with three ribs and seven joints.) Pores regular, hexagonal.

Dimensions.—Length of the shell (with seven joints) 0.25. Length of each joint 0.02 to 0.025, of the last joint 0.12; breadth 0.14.

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

3. Stichopera serrata, n. sp.

Shell bottle-shaped, with eight deep strictures. The first eight joints are little different in length, and form together a slender cone, while the last joint is four times as long (half as long as this cone), and subspherical. Cephalis conical, with a slender, prismatic horn of three times the length. Along the whole shell arise three divergent, serrate ribs, which disappear towards the hemispherical, basal pole. Pores subregular, hexagonal.