164 PALEONTOLOGY OF THE EUEEKA DISTEICT. 



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, Edmondia f 

 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: 



Actmopteria Boydi. 

 Paracyclas occidentals. 

 Pteriuea flabella. 

 Leiopteria Eafinesqui. 

 San gum elites 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. 



