80 PALEONTOLOGY OF THE EUREKA DISTRICT. 



Casts of two species of Murchisonia occur in the upper beds of the 

 Pogonip Group of the Eureka District. One is slender, elongate, and 

 formed of many whorls, resembling the eastern species Murchisonia gracilis 

 Hall (Pal. N. Y., vol. i, p. 181, pi. xxxix, figs. 4-c) ; the other is a much 

 larger, stronger species, more like Murchisonia bellicincta of the Trenton lime- 

 stone of New York. The specific relations of either are not determined. 



Genus PLEUROTOMARIA Defiance. 



Pleurotomaria Lonensis, u. sp. 

 Plate xi, fig. 22. 



Shell rather small, depressed conical; the apical angle about 110; 

 volutions three or four, each flattened above to within a short distance of 

 the sharp mesial angle, where a narrow groove extends around on the lower 

 volution, becoming obsolete on the second volution; suture in the cast strong 

 and channeled; lower side of body volution sloping quite rapidly in from 

 the mesial angle, a little concave just within the angle, and then gently con- 

 vex to the umbilicus, which is rather small. Aperture rhombic-subquadrate, 

 as far as can be determined from the form of the body volution. 



Surface unknown except by the presence of rather strong revolving 

 lines on the lower side of the body volution. 



This species is distinct from any known to us. 



At the same horizon and localities there is another species that may be 

 referred to this genus; it is a larger and more robust form, having the whorls 

 more convex above, flattened below on the body volution, and an acutely an- 

 gular periphery at the union of the upper slope of the whorls and the base; 

 this latter feature also occurs in P. Lonensis. 



Formation and localities. Upper beds of the Pogonip Group, Lone 

 Mountain, 18 miles northwest of Eureka; at the south end of Fish Creek 

 Mountain exposure of the Pogonip, and on east slope of ridge east of Ham- 

 burg mine, Eureka District, Nevada. 



On the north end of Pogonip Ridge, White Pine District, Nevada, this 

 species is abundant and reaches a larger size than at Lone Mountain. 



