158 PALEONTOLOGY OF THE EUBEKA DISTRICT. 



to the sides or becoming slightly depressed, flattened below the center, and 

 more or less sinuate on the lower part. Beak acute and closely incurved 

 over that of the opposite valve. Dorsal valve uniformly convex, the con- 

 vexity increasing with the size of the individual ; a broad, hardly percep- 

 tible mesial fold is seen on the lower part of the valve only in the larger 

 shells. 



Surface marked by a few obscure plications on the mesial fold and in 

 the sinus that become obsolete midway to the apex. On the surface of 

 well-preserved specimens concentric striss occur which at intervals are 

 crowded together, forming slight ridges. 



There is considerable variation between young and adult specimens. 

 Those 15 mm in length show but a trace of the mesial fold and sinus or of 

 the surface plications; the ventral valve is more uniformly convex, less de- 

 pressed below, and subequal to that of the dorsal valve. In this condition 

 it bears a close resemblance to the young shells of some of the larger forms 

 of the genus Meristella. 



This species is closely related to R (.) Kelloggi Hall (Pal. N. Y., vol. 

 iv, p. .'^61, pi. Ivii, figs. 112) of the Chemung Group of New York, the char- 

 acter of the mesial fold and sinus and the surface plications serving to dis- 

 tinguish it from that species. 



Formation and locality Devonian limestone. Rescue Hill, near Rescue 

 Cafion, Eureka District, Nevada. 



Rhynchonella (Leiorhynchus) slnuatua Hall. 



Plate xiv, fig. 5. 

 Leiorhynchus sinuatus Hall, 1867. Pal. N. Y., vol. iv, p. 362, pi. Ivii, figs. 13-17. 



The specimens of this species from the Chemung Group of New York 

 are all more or less compressed, and none show the true convexity of the 

 shell and surface plications. With this in view, the perfect and uncom- 

 pressed specimens from the limestone of the Eureka District are specifically 

 identical with them. There is considerable variation among the specimens 

 from the same bed; some are more elongate than the New York forms, 

 while others are almost a counterpart of them. 



