ORTMANN: monograph of the naiades of PENNSYLVANIA. 91 



Genus Elliptio Rafinesque (1820). 



Ortmann, 1912, p. 265; Simpson, 1914, p. 586 (as section of Unio). 



Type Unio nigra Rafinesque. 



Five species and one variety are found in Pennsylvania (one of them somewhat 

 doubtful as to its presence in the state). 



Key to the Pennsylvanian Species and Variety of Elliptic. 



a I. Shell very large, rhomboid-ovate, not elongated, with a sharp posterior ridge. Posterior slope (at 



least in the young) with radiating wrinkles. (Western shell.) E. niger. 



a -2. Shell larger or smaller, elongated ovate, or subtrapezoidal, with ill defined or no posterior ridge. 

 Posterior slope not wrinkled. 

 bi. Shell rather large, elongated ovate, heavy, not subtrapezoidal, somewhat inflated or subcom- 

 pressed. (Western shells.) 

 Cj. Shell larger, subcompressed. Epidermis dark colored, with obscure growth-lines. 



E. dilalatus. 

 C2. Shell smaller, more swollen and thus more nearly subeylindrical. Epidermis of lighter 



color, with more distinct and more regular growth-lines E. dilaiatvs sterkii. 



bi. Shell moderately large or small, subtrapezoidal, more or less elongated, and more or less com- 

 pressed. (Eastern shells.) 

 Ci. Shell moderately large, subtrapezoidal, slightly elongated, not much pointed behind. 



E. violaceus. 

 Co. Shell moderately large or small, subtrapezoidal, but much elongated, so as to become lance- 

 shaped, pointed behind, 

 di. Shell rather small, upper and lower margins nearly parallel; greatest height in the 



middle portion E. cwpreus. 



di. Shell somewhat larger, upper and lower margins not subparallel; greatest height more 

 anteriorly E. fisherianus 



Elliptio nicer (Rafinesque) (1820). 



Unio crassidens Lamarck. Simpson, 1914, p. 606. 



Plate VIII, fig. 1. 

 Records from Pennsylvania: 



CaU, 1885 (Allegheny River). 



Harn, 1891 (western Pennsylvania). 



Clapp, 1895 (Allegheny Co.). 



Marshall, 1895 (Allegheny River, Warren Co.).*« 



Rhoads, 1899 (Ohio River, Coraopolis, Allegheny Co., and Beaver, Beaver Co.). 



Ortmann, 19096, p. 197. 



Characters of the shell: Shell large and very heavy'. Outline ovate-rhomboid, 

 rather variable, shorter or longer, but always longer than high, but rarely almost 



'•* This record is doubtful. I have never seen tliis striking shell in the Allegheny above Oil City. 



