Maryland Geological Survey 213 



Class PELECYPODA 



Order TELEODESMACEA 



Superfamily CYRENACEA 

 Family CYRENIDAE 



Genus CYRENA Lam. 

 Cyrena marylandica sp. nov. 



Plate XXI, Figs. 8, 9 



Description. — Shell subtriangular, thin, flattened, obscurely concen- 

 trically ridged, inequilateral ; the beaks low. 



The fragmentary specimens of this species indicate that it belongs to 

 the genus Cyrena. 



Length, 12 mm. ; height, 6.5 mm. 



Occurrence. — Arundel Formation. x\rlington, Anne Arundel County, 

 Maryland. 



Collection. — Maryland Geological Survey. 



Order PRIONODESMACEA 



Superfamily NAIADACEA 

 Family UNIONIDAE 



Genus UNIO Retzius 



IJnig patapscoensis sp. nov. 

 Plate XXI, Fig. 7 . 



Description. — Shell subovate, elongate, thin, flattened, beak about one- 

 third distance from anterior to posterior end, and low. 



The single valve found is a cast Avhich shows clearly the characteristic 

 form of the shell. 



Length, 35 mm.; height, 20 mm. 



Occurrence. — Patapsco Formation. White House Bluff, Fairfax 

 County, Virginia. 



Collection. — U. S. National Museum. 



