PTEROPODA. 
199 
The longest specimens are about thirty-five millimetres, and the greatest 
width near the base is about thirteen millimetres. The vertical diameter is 
about half as great as the lateral diameter. 
In comparison with H. ligea, the form is more acute, its angularity more 
distinct, and the base narrower in proportion to the length. In general form, 
this species is not unlike H. discors, of Barrande (pi. 16, figs. 1-3), and the 
separated ventral portions of the young shells of our species resemble those of 
H. obvius, Barrande, as figured on plate 15, fig. 22 (Sil. Syst. du centre de 
la Boheme, vol. iii). 
Formation and localities. In the semi-calcareous shales of the Hamilton 
group, on the east and west sides of Cayuga lake; Bellona, Yates county; 
Pratt’s Falls and Delphi, in Onondaga county; and Sherburne creek, Chenango 
county, N. Y. 
Hyolithes striatus. 
PRATE xxxn, FIGS. 31, 32, 33, 31. 
Hyolithes striatus, Ha.ll. Illustrations of Devonian Fossils : Pteropoda, pi. 27, figs. 8, 9, 12. 1876. 
Form that of an extremely elongated triangular pyramid, which becomes 
gradually attenuated towards the apex, with scarcely a perceptible 
curvature. Transverse section triangular, more than twice as wide as 
high, the margins thin, and the sides apparently a little unecpial. The 
dorsal angle well defined, and in one specimen a little rounded. The 
ventral face nearly flat, or with a moderate convexity, much extended 
and regularly rounded in front; the curvature in a longitudinal direction 
is scarcely perceptible. Dorsal face convex, angular, subcarinate along 
the centre, with the sides nearly plain; the median angle becoming more 
defined towards the apex. Aperture oblique, being much extended on 
the ventral side; the dorsal margin is unknown, the specimens being 
imperfect. The shell is thin, and in our specimens, very imperfectly 
preserved. No septa are perceptible. The operculum referred to this 
species is somewhat semi-elliptical, the lateral diameter being nearly twice 
