FOSSILS OF THE LOWER SILURIAK 237 



part of the last volution on the specimen examined. No surface-markings 

 can be detected. 



The specimen is quite imperfect, and is only given on account of its 

 low geological horizon; the most of the species hitherto recognized being 

 from the Trenton or Hudson River groups. The species differs from all 

 others of the genus yet described in the short compact volutions. 



Formation and locality. — In the granular limestones, Pogonip Mountain, 

 west side, White Pine District, Nevada; of the age of the Quebec group. 

 Collected by A. J. Brown, esq. 



Genus CYRTOLITES Conrad. 

 Cyrtolites sinuatus u. sp. 



Plate I, figs. 23-24. 



Shell small, laterally compressed; composed of about one and a half 

 to two volutions, which are closely coiled, but not embracing. Volutions 

 acutely triangular; the dorso-ventral diameter about one-half greater than 

 the lateral diameter; sides of the outer one marked by a broad, shallow 

 depression or sinus a little within the margin, between which and the 

 umbilicus the surface is rounded. Umbilicus broad, exposing the inner 

 volutions; the sides abrupt or nearly vertical except on the edge, which is 

 shghtly rounded. Surface of the shell unknown. 



The species is characterized by the vertical margins of the umbilicus, 

 and the broad, shallow, depressed sinus of the outer half of the volution, 

 giving a somewhat concavo-convex curvature to the surface between the 

 umbilicus and the outer edge, or keel. In this respect, it differs from all 

 other species with which we are acquainted. 



Formation and locality. — In the granular limestone, on the west side of 

 Pogonip Mountain, White Pine District, Nevada. Collected by A. J. 

 Brown, esq. 



CEUSTAOEA. 



Genus CONOCEPHALITES Zenker. 



CONOCEPHiXITES SUSCORONATUS n. Sp. 



Plate II, fig. I. 



Glabella short, conical, with straight lateral margins, regularly con- 



9^ 



