236 MEMOIRS OF THE CARNEGIE MUSEUM 



but I never have seen it in the upper Monongahela (West Fork River) in West 

 Virginia. Likewise in the tributaries, it only goes up for a certain distance, and 

 then rather suddenly stops. This is the more remarkable, since it is, where present, 

 the prevailing species, outnumbering all other species combined, and then dis- 

 appears entirely sometimes within a few miles. In the Little Beaver I have never 

 seen it above Cannelton. It is plentiful at Edinburg in the Mahoning, but at 

 Hillsville, a few miles farther up, I saw onl.y a single dead shell, and it is absent 



Fig. 24. 

 • Actinonaias ligamentina. 



in the Ohio part of this river (Dean, 1890). It is plentiful at Pulaski in the She- 

 nango, but above Sharon there is no trace of it. It goes into the Connoquenessing 

 to EUwood City, and enters the mouth of SlipperjTock Creek, but is not found 

 farther uj). It used to be found in the Kiskiminetas, but our material from this 

 stream is scanty. A dead shell was found in the Loyalhanna at Idlepark. In 

 Crooked Creek it occurs only at the mouth; in French Creek it extends up to 

 Cambridge Springs, and in Connewango Creek as far up as Russell. 



Thus it is clear that A. ligamentina prefers the larger rivers. It is found here 

 in various environmental conditions, but is apparently best fitted for rough parts, 

 riffles with strong currents and heavy gravel and rocks. Baker (1898a) says that 

 it is found in muddy and sluggish rivers in soft mud, but this is decidedly not the 

 case in our region. Call (1900) also calls it a "mud-loving species." In the Ohio 

 below Pittsburgh and far down toward Cincinnati it is the form mainly composing 

 the shell-banks. 



