14 
PALJEONTOLOGY OF NEW YORK. 
is ventricose, rapidly expanding from the first, giving an obliquely 
conical form. Aperture nearly circular or broad oval; peristome sinuate, 
the lines of growth and fine striae conforming in direction to the outline 
of the margin. Remains of revolving striae are sometimes traceable, 
when the shell is not exfoliated. Besides the concentric and less con¬ 
spicuous revolving striae, the surface is studded with numerous nodes or 
small spines—the latter preserved only when the shell has been imbedded 
in soft shale, and quite separable from the rock; when imbedded in lime¬ 
stone, the spines and exterior shell are removed with the matrix. 
In this species the shell varies from half an inch to an inch and a quarter in 
length, and in a large specimen, the greatest diameter of aperture is one inch. 
In this form we have a miniature representation of the P. dumosum . and it 
might perhaps be considered as the young of that species if occurring in the same 
formation. Since, however, it is known only in a higher geological horizon, it 
must be regarded as a distinct species or a degenerate condition of P. dumosum. 
Formation and localities. In shales of the Hamilton group; Moscow and Lud- 
lowville; and in Tully limestone, at Ovid, N. Y. 
Platyceras dumosum. 
PLATE V, FIGS. 11-16, and PLATE VI, FIG. 1. 
Platyceras dumosum, Conrad. Third Ann. Rep. Pal. Dept. [N. Y.] Surv., p. 205. 1840.. 
“ “ (Conr.) Hael. Twelfth Rep. N. Y. State Cab. Nat. Hist., p. 19. 1859. 
“ “ “ Descriptions of New Species of Fossils, etc., p. 9. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 87. 1862. 
“ “ “ Illustrations of Devonian Fossils: Gasteropoda, plates 5 and 6. 1876. 
Compare Platyceras imdtispinosum, Meek. Proc. Acad. Nat. Sci., Philadelphia, p. 17. 1871. 
“ “ “ “ Geolog. Surv. Ohio: Pal., vol. 1, p. 210, pi 20, f. 7. 1878. 
Shell subovoid, arcuate, extremely ventricose when full-grown; the length 
from the apex to the anterior margin of the aperture greater than the 
height. Apex minute, closely enrolled for a single volution or more, 
when the body-volution becomes free and rapidly expanded, spreading 
