164 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Dorsal valve not quite as convex as the ventral; most elevated at the 
center, from which point it curves regularly to the margins; beak incurved 
beneath the deltidial plates of the ventral valve. 
Outer surface exfoliated. Shell structure punctate. 
The generic reference is based entirely on external form and character; 
nothing is known of the interior characters, except two elongate, median, 
muscular imprints on the ventral valve. The specific relations appear to be 
nearest some forms of Cryptonella planirostra of the Hamilton Group of New 
York. A direct comparison with the types of that species, and also of C. 
rectirostra Hall, leads us to think that the Nevada form is distinct from each, 
Formation and locality—Upper Devonian; south end of the Pinon 
Range at The Gate, northwest of Eureka, Nevada. 
LAMELLIBRANCHIATA. 
Our knowledge of this class of shells in the Devonian Group of the 
area embraced within the Rocky Mountains has been up to the present time 
very limited, Mr. Meek having described but three species, viz, Hdmondia ? 
Pinonensis, Aviculopecten catactus, and Lunulicardium fragosum, the types of 
which were collected by the geologists of the Fortieth Parallel Geological 
Survey,in Central Nevada. To this list we have added twenty-three genera, 
represented by thirty-five species. Of these, eight species are identical 
with species in the Eastern Paleozoic area of Ohio and New York, viz: 
Actinopteria Boydi. 
Paracyclas occidentalis. 
Pterinea flabella. 
Leiopteria Rafinesqui. 
Sanguinolites rigidus. 
Sanguinolites? Sanduskyensis. 
Sanguinolites ventricosus. 
All of the twenty-three genera, with the exception of Posidonomya, 
are identical with Devonian genera of the Eastern United States. 
In the systematic catalogue at the end of this volume the vertical range 
of the various species in the Devonian Group of the Eureka District is 
given. 
