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, Barraxde, as figured on plate 15, fig. 22 (Sil. Syst. du centre de 

 la Bohlme, 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. 



PLATE XXXII, TIGS. 31, 33, 33, 34. 

 HjfoHtim striatus. Hall. 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 unequal. 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 ve'ntral 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 



