86 
NATJTIL07DEA. 
Genus DISCITES (de Haan^, M‘Coy^ 
{Nautili Ornati (pars), de Koninck^ ; Nautili Disciformes, de Koninck^ ; 
Discitoceras, Pselioceras, Hyatt ^.) 
Fig. 11. 
Biscites coonpressus. — a. Lateral view of a nearly perfect specimen, showing 
faint lines of growth on the body-wliorl, and the characteristic cancellated 
sculpture in the young shell, h. Peripheral view, showing the deep sulcus. 
Drawn from a specimen in the Collection. About two thirds of the 
natural size. 
Gen. Char. Shell discoid, much compressed, the umbilicus wide, 
shallow, and exposing all the inner volutions and the small central 
vacuity ; the volutions only just in contact, or very little embracing, 
narrow, increasing gradually in size, quadrangular in section, 
channelled or flattened on the periphery. Body-chamber occupy- 
ing one half of the last whorl. The latter becomes separated from 
the rest of the shell for a distance of | to inch in adult shells. 
The dorsal side is marked by a median ridge bordered by two 
grooves corresponding with the ventral channel and its bordering 
ridges. Septa straight, or slightly arcuate on the sides and peri- 
1 Monographiam Ammoniteorum et Gouiatiteorum, 1825, p. 41. 
^ Synop. Carboniferous Foss, of Ireland, 1844, p. 17. 
^ Calc. Carb. de la Belgique, 1878 (Annales du Mus. Eoy. d’Hist. Nat. de 
Belgique, tom. ii.), p. 90. 
^ Ibid. 
® Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 292; ibid. p. 299. 
