The genus Lamprodiscus, and the following nearly allied Lampromitra, differ from all preceding Sethopilida in the complete connection of the three thoracic feet by lattice-work, so that they are imbedded in the thorax-wall as prominent ribs and are not prolonged beyond the margin as free feet. The shell is commonly very flat, conical or pyramidal, sometimes nearly discoidal. The margin of Lamprodiscus is simple, smooth.
1. Lamprodiscus monoceros, Ehrenberg.
Shell smooth, with deep collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 8. Cephalis spherical, hyaline, without pores, with an oblique conical horn of the same length. Thorax flat, campanulate, nearly hemispherical, with convex lateral outlines, and regular hexagonal meshes, increasing gradually in size towards the mouth. Bars very thin. Peristome smooth.
Dimensions.—Cephalis 0.02 diameter; thorax 0.1 long, 0.16 broad.
Habitat.—Western Tropical Pacific (Philippine Sea), Station 200, surface.
2. Lamprodiscus coscinodiscus, Ehrenberg.
Shell smooth, with sharp collar stricture. Thorax of the same form and structure as in the preceding species, differing from it mainly in the structure of the smooth circular margin, which is composed of a ring of very small square pores. Length of the two joints = 1 : 4, breadth = 1 : 8. Cephalis with small hexagonal pores, without horn or with a short rudimentary horn. Lateral outlines of the campanulate thorax in the upper part concave, in the lower convex.
Dimensions.—Cephalis 0.02 diameter; thorax 0.08 long, 0.16 broad.
Habitat.—Tropical Pacific, Stations 206, 224, 266, &c., surface.
3. Lamprodiscus tricostatus, n. sp.
Shell smooth with deep collar stricture. Length of the two joints = 1 : 3, breadth = 1 : 7. Cephalis spherical, with an oblique conical horn of twice the length and small circular pores. Thorax flatly conical, twice as broad as high, with straight lateral outline, and regular hexagonal meshes, increasing gradually in size towards the mouth; bars very thin. Peristome or margin of the basal mouth circular, smooth. Very similar to Theopilium tricostatum (Pl. 70, fig. 6), but without abdomen. Differs from the two preceding species mainly in the conical form of the thorax and the less delicate network.
Dimensions.—Cephalis 0.03 diameter; thorax 0.1 long, 0.2 broad.
Habitat.—Cosmopolitan, Mediterranean, Atlantic, Indian, Pacific; surface.
