ORTMANN: monograph of the naiades of PENNSYLVANIA. 97 



Remarks: I know of only two species in Pennsylvania, with which the present 

 species might be confounded according to the general shape: Ellipsaria fasciolaris 

 (Rafinesque) and Eurynia recta (Lamarck). The former is easily distinguished 

 l)y the light, yellowish brown color of the epidermis, variegated with green rays and 

 blotches; the latter is a straighter shell, more pointed behind, with a greenish 

 black and shining epidermis. 



Elliptio dilatatus is variable chiefly in size. In the larger rivers general!}^, 

 and sometimes also in smaller creeks, it grows to a considerable length; while in 

 other streams, chiefly those of the mountains, it remains rather smaU. Its general 

 shape is rather uniform: it always is an elongated shell, produced and tapering 

 behind, with no indication of a trapezoidal outline, and with a bluntly pointed 

 posterior end. Its nacre is very variable in color, but while in the Ohio and Alle- 

 gheny all shades are found, and shells with white nacre are quite abundant, in 

 other sections, as for instance in the whole Beaver-drainage, shells with light- 

 colored nacre are extremely rare. There is no tendency to form local races, except 

 that a dwarfed form prevails in the mountain-streams. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Ohio-drainage: 

 Ohio River, Smiths Ferry, Shippingport, Cooks Ferry, and Industry, Beaver Co.; Coraopolis (S. N. 



Rhoads) and Neville Island, Allegheny Co. 

 Little Beaver Creek, Cannelton (Miss Vera White), Darlington, and New Galilee, Beaver Co.; Enon 



Valley, Lawrence Co. 



Beaver-drainage : 

 Beaver River, Wampum, Lawrence Co. (G. H. Clapp & H. H. Smith). 

 Conuoquenessing Creek, Ellwood City, Lawrence Co. (G. L. Simpson, Jr.). 

 Slipperyrock Creek, Wurtemberg and Rose Point, Lawrence Co. 

 Wolf Creek, Grove City, fiercer Co. 



Mahoning River, Mahoningtown, Coverts, Edinburg, and Hillsville, Lawrence Co. 

 Neshannock Creek, Eastbrook and Volant, Lawrence Co.; Leesburg, Mercer Co. 

 Shenango River, Harbor Bridge and Pulaski, Lawrence Co.; Sharpsville, Clarksville, Shenango, and 



Jamestown, Mercer Co. 

 Pymatuning Creek, Pymatuning Townsliip, IVIercer Co. 

 Little Shenango River, Greenville, Mercer Co. 



A llegheny-drainage : 



Allegheny River, Natrona, .Allegheny Co.; Schenlej% Aladdin, Godfrey, Johnetta, Kelly, Mosgrove, 

 Templeton, and Parkers Landing, Armstrong Co.; Walnut Bend, Venango Co.; Tionesta and 

 Hickory, Forest Co.; Warren, Warren Co.; Larabee, McKean Co. (Dennis Dally). 



Loyalhanna River, Idlepark and Ligonier, Westmoreland Co.*° 



Yellow Creek, Homer, Indiana Co. 



'" Dead shells have been seen in the Conemaugh River, at New Florence, Westmoreland Co, 



