Lise. PALEONTOLOGY OF THE EUREKA 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 striae occur which at intervals are 
crowded together, forming slight ridges. 
There is considerable variation between young and adult specimens. 
Those 15™" 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 (L.) Kelloggi Hall (Pal. N. Y., vol. 
iv, p. 361, pl. lvii, figs. 1-12) 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 
Canon, Eureka District, Nevada. 
Rhynchonella (Leiorhynchus) sinuatus Hall. 
Plate xiv, fig. 5. 
Leiorhynchus sinuatus Hall, 1867. Pal. N. Y., vol. iv, p. 362, pl. lvii, 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. 
