FOSSILS OF THE DEVONIAN. 



167 



Genus LEPTODESMA Hall. 



Leptodesma traiisversa, n. sp. 

 Plate v, fig. 13. 



General form transversely ovate or oblong. General surface of the 

 left valve strongly convex, but not gibbose. Hinge straight and continued 

 posteriorly to the acute termination of the wing, which appears to have had 

 a short spinose extension. Beaks small, arching over the cardinal line. 



Surface marked by numerous concentric lines of growth. 



Interior characters unknown. 



Dimensions: height, 7 mm ; breadth, 12 mm ; convexity of left valve, 2.5 mm . 



With the exception of Leptodesma naviforme Hall (Pal. N. Y., vol. v, 

 pt. 1, p. 200), of the Chemung Group of New York, this species is more 

 oblique and transverse than any species known to me. 



Formation and locality. Upper Devonian, Chemung horizon, at The 

 Gate, northwest of Eureka, Nevada. 



Genus LIMOPTERA Hall. 



Limoptera sarmenticia, D. sp. 

 Plate v, figs. 3, 3 a, b. 



Shell oblique, subovate in outline within the extension of the posterior 

 wing. Left valve strongly convex. Hinge-line straight ; ligamental area 

 unknown. Beak of left valve elevated and incurved over the cardinal line. 



Surface marked by concentric lines of growth, and not very strong 

 radiating striae. 



Interior characters unknown. 



Dimensions: height of a narrow specimen, 3.25 cm ; breadth, 2.5 cm ; con- 

 vexity of left valve, 1.25 cm ; of a broad specimen: height, 3 cm ; breadth, 3 cm ; 

 convexity of left valve, 1.25 cm . 



This is unlike any species of the genus known to me. The variation 

 in form among the different specimens is considerable, as is shown by figs. 

 3 a and 3 1). The surface striae are usually absent in the cast. 



