ORTMANN: monograph of the naiades of PENNSYLVANIA. 



199 



Remarks: Although very variable in outline and color, this species is easily 

 recognized by the elliptical shape, and the rudimentary condition of the hinge. 

 If gravid females are at hand, the marsupial structure unmistakably indicates the 

 genus. Only Anodontoides ferussacianus might be confounded with this species, 

 but the shell of the latter is generally thinner, and the nacre is more bluish white, 

 with very little pure white, and further the beak-sculpture is much finer. 



Specimens with well-defined rays have been called pavonia Lea. The type 

 localit}^ of this is Little Beaver Creek in Ohio. I possess many specimens from 

 this creek in Pennsylvania, and among them are many which correspond to pavonia, 

 but they are connected by all possible intergrades with the normal *S'. edentulus. 



Fig. 20. 

 • Strophittcs edentulus (western half of State of Pennsj'lvania). 



Such brightly colored individuals may turn up anywhere, on the western as weU 

 as on the eastern side of the Alleghenies, and are always found associated with 

 the normal form."' 



There is little inclination to foi-m local races, although under certain conditions 

 and at certain localities the specimens look rather uniform. Thus in the moimtain- 

 streams on the western side of the mountains, there is a small, often more elongated 

 race of S. edenhdus, and the Allegheny River in general, does not produce very 

 large, but rather heav^'-sheUed specimens. In the Beaver-drainage this species 

 is much larger on the average. Strangely enough the largest specimens on record 

 are from the Atlantic-drainage, in the headwaters of the West Branch of the 



"' Wilson & Clark (1912a, p. 48) believe that the better development of rays (in pavonia) is corre- 

 lated with the clearness of the water, and I think that this is right. 



