^^18'jo"''] PROCEEDINGS OF THE NATIONAL MUSEUM. 269 



The shell occurs in association with Dil-eUoccphalus hartti, £). speciosus, 

 Lingnlepis acuminata., etc.. of the Upper Cambrian fauna. It is not a 

 true Trochus, and in the photograph plate illustrating the Potsdam 

 fauna of Saratoga Countj'^, New York, that I had prepared in 1883, it 

 bears the name BilUiujsia saratogensis. This generic name was used in 

 a list of species in 188C,* but no publication of the description of the 

 species has yet appeared. The name Billingsia having been used the 

 species is provisionally referred to Trochus until further comparisons 

 can be made with Eotrochus and other genera of the Trochida^. 



Formation and locality. — Limestone of the Potsdam terrane, 4 miles 

 west of Saratoga Springs, New York. Collector, C. U. W. 



Nat. Mus. Cat., Invert. Foss., 23847. 



Hyolithes attenuatus sp. uov, 

 PlatL- XX, Fij48 11, llrt. 



Form an extremely elongate triauirnlar pyramid. Transverse section 

 subtriangular, width and depth as three to two. The dorsal side nearly 

 Hat, with the exception of a shallow, narrow, median groove. Ventral 

 face convex, with the ventral angle broadly rounded. Surface appar- 

 ently smooth. 



In its rounded ventral side this species resembles H. princeps of the 

 Lowt'T Cambrian. 



Formation and locality. — Up])er Cambrian limestone of the Highland 

 Range section, central Nevada. Collector, C. D. W. 



Nat. Mus. Cat. Invert. Foss., 23850. 



Hyolithes curvatiis «]>. iiov. 

 Plate XX, Figs. 7, 7a. 



Shell, an elongate curved pyramid that becomes attenuated towar*ls 

 the apex. Transverse section triangular, with the width and height 

 subequal. Ventral face very convex, strongly angular at the cen.ter, 

 sides slightly rounding. Dorsal face slightly convex or nearly Hat at the 

 nmrgin and rising towards the center. Dorso-ventral angles shar{»ly 

 and clearly defined. Anterior extension of the dorsal surface and form 

 of aperture unknown. Shell apparently thick. Surface of the sliell 

 marked by strong concentric lines of growth near the aperture, and 

 longitudinal lines that separate fine, rounded ridges, not much wider 

 than the depressions between them. These are not shown in the figure. 



The tendency to curvature is shown in several species illustrated by 

 M. Barrande, but none is so marked as in the species under considera- 

 tion. 



*Bull, U. S, Geol. Surv., No. 30, 1886, p, 21, 



