9« PALEONTOLOGY OP NEW- YORK. 



the posterior margin or less than one-fourth the length of the shell 

 therefrom, prominent, being from less than one-eighth to one-quarter 

 of an inch above the plane of the margins. Ventral valve slightly con- 

 cave ; apex excentric ; foramen large, oval, with the margins deeply 

 depressed. Shell comparatively thick and strong. 



ScRFACK marked by fine concentric lines, which are very faint in young 

 shells, but become stronger and rise into distinct sharply elevated striae 

 in older specimens. 



Where partially exfoliated, the shell shows intermediate fine radiating 

 striae ; and in older specimens, the interior of the shell, and likewise 

 the cast, is marked by strong radiating vascular impressions. The 

 structure of the shell is strongly lamellose. The casts of the dorsal 

 valve show a narrow longitudinal muscular impression on the anterior 

 side of the beaks. The length varies from one-eighth to one inch. 

 For these specimens, I am indebted to Dr. J. S. Newberry. 



Geological formation and locality. Abundant in a ferruginous band about 110 

 foet below the Conglomerate at Cuyahoga falls, and in the green shale and shaly 

 sandstone at Akron, Ohio. 



GEXL'S CRMIA (Retzius). 



Up to the present time, the Genus Crania has not been recognized in the 

 New-York collections, from any rock below the Schoharie grit. 



The extensive and long continued explorations in the^Lower Helder- 

 berg group, which resulted in the discovery of many rare and obscure 

 fossils of that formation, we may suppose would have brought to light any 

 species of this genus which might have lived in the area of investigation. 

 Still we are far from being warranted, by this negative information, in 

 the inference that this genus did not exist in the preceding periods in the 

 New-York strata, since we know of its occurrence in rocks of the age of 

 the Niagara group in Indiana. At this time we know of but two indivi- 

 duals in the Schoharie grit, notwithstanding that collections have been 

 made from that rock during the past twenty-five or thirty years. 



