FOSSILS OF THE LOWER SILURIAN. 



75 



of a distinct name, but until there is more evidence than at present, we pre- 

 fer to recognize it as coming within the limits of the eastern species. 



Formation and locality. Pogonip Group at Lone Mountain, 18 miles 

 northwest of Eureka, and on Surprise Peak, Eureka District, Nevada. It 

 also occurs at the same horizon on Pogonip Ridge, White Pine District, 

 Nevada. 



Genus STREPTORHYNCHUS King. 



Streptorhyiictms minor, u. sp. 

 Plate xi, fig. 9. 



Shell small, transverse, semi-oval ; hinge line fully equaling the greatest 

 breadth ; lateral extremities nearly rectangular. 



Ventral valve moderately convex along each side of a rather broad 

 mesial depression, extending from the umbo to the front margin; postero- 

 lateral regions flattened within the margin ; beak minute and scarcely to be 

 distinguished from the cardinal margin. Dorsal valve unknown. 



Surface of ventral valve ornamented with rather fine radiating striae 

 that increase by intercalation towards the front margin. 



Length of specimen, 6 mm ; breadth, ll mm ; convexity, about 1.25 mm . 



This little shell presents the characters of a resupinate Strophomena, 

 and is therefore placed under the genus Streptorhynchus. It may be com- 

 pared with young shells of Streptorhynchus sinuatus Emmons (Pal. Ohio, vol. 

 1, p. 87, pi. v, figs. 5 a-/, 1873), but it appears to be a distinct species from 

 any described. 



Formation and locality. Pogonip Group, upper beds, at Lone Mountain, 

 18 miles northwest of Eureka, Nevada. 



Genus TRIPLESIA Hall. 



Triplesia calcifera Billings. 



Plate xi, figs. 7, 8. 



Camerella calcifera Billings, 1861. Canadian Nat. and Geol., vol. vi, p. 318, figs. 3 a-c. 

 -Geol. Canada, p. 231, figs. 247 a-c, 1863. Pal. Foss., vol. i, p. 220, 1865. 



There is considerable variation among the specimens referred to this 

 species in the collection, and two species appear to be indicated. In one 

 the mesial depression is shallow with broadly-rounded sides, and in the 

 other it is deeper and more angular. In the dorsal valves the variation is 



