Cephalis hemispherical, with irregular roundish pores and a prismatic club-shaped horn of twice the length, the three edges of which are denticulate and fenestrated. Length of the two joints = 1 : 3, breadth = 1 : 4. Thorax thorny, with three broad triangular, fenestrated and nodulated ribs, which are separated by three large ovate holes (twice as long as the cephalis) and have their prominent distal ends connected below by a circular ring of lattice-work. Peristome constricted, as broad as the thorax, with a corona of short spines.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.08 long, 0.12 broad.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
Genus 541. Lamprodiscus,[[158]] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 831.
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three divergent lateral ribs in the wall of the flat, conical, discoidal, or pyramidal thorax. Cephalis with a horn. Peristome smooth, without corona of spines.
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.
Lamprodiscus monoceros, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 295, Taf. vii. fig. 2.
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.