328 MEMOIRS OF THE CARNEGIE MUSEUM. 



that it cannot be confounded with any other species. The male also is quite 

 well-defined by its subtriangular shape, strong posterior ridge, and truncate pos- 

 terior slope, and also its color-pattern. However, to a certain degree the male 

 resembles Amygdalonaias truncata (Rafinesque) but the latter is a higher and 

 more compressed shell, with the posterior ridge sharper, chiefly in the region of the 

 beaks, and with the posterior slope narrower and less distinctly truncate. 



There is a good deal of variation in the shell of Truncilla triquetra. Aside 

 from the general outline, which is more subtrapezoidal in young shells, and more 

 subtriangular in old ones, there is variation in the elongation of the shell. In old 

 males the posterior end is often considerably drawn out. Both males and females 

 vary greatly in diameter and in the width of the posterior slope, which in some 

 old females becomes really freakish. There is also great variation in the color- 

 pattern, and the rays and the spots are hardly ever alike in any two specimens. 



The Lake Erie form of this species does not seem to differ from the normal 

 type. I have only few specimens from the lake, which compared with specimens 

 from the Ohio are of about medium size, and seem to be slightly lighter in color. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Ohio River, Neville Island, Allegheny Co."'" 



Beaver River, Wampum, LawTence Co. (G. H. Clapp & H. H. Smith) .^" 



Mahoning River, Mahoningtown and Edinburg, Lawi'ence Co. 



Shenango River, Pulaski, Lawrence. Co.; Sharpsville, Clarksville, and Shenango, Mercer Co. 



Pymatuning Creek, Pymatuning Township, Mercer Co. 



Allegheny River, Aladdin, Godfrey, Johnetta, Kelly, Mosgrove, and Templeton, Armstrong Co. 



Crooked Creek, Rosston, Armstrong Co. 



French Creek, Utica, Venango Co.; Meadville and Cambridge Springs, Crawford Co. 



Conneaut Outlet, Conneautlake, Crawford Co. 



Leboeuf Creek, Waterford, Erie Co. 



Dunkard Creek, Mount Morris, Greene Co. 



Lake Erie, Presque Isle Bay, Erie, Erie Co. 



Other localities represented in the Carnegie Museum: 



Lake-drainage : 

 Sandusky River, Fremont, Sandusky Co., Ohio (C. Goodrich). 

 Swan Creek, Toledo, Lucas Co., Oliio (C. Goodrich). 



Ohio-drainage: 

 Ohio River, Portland, Meigs Co., Oliio. 

 Tuscarawas River, Oliio (Holland collection). 

 Miami River, Oliio (Juny collection). 



^■^ A dead shell has been seen at Industry, Beaver Co. 



"' A dead shell has been seen in SlipperjTock Creek, at Wurtemberg, Lawrence Co. 



