STATION IN FRESH-WATER MUSSELS. 291 



have found in the Knoxville region, and what I have from the Ten- 

 nessee in northern Alabama, should all be classed with A. costata. 



QuADRULA PUSTULOSA (Lea) (Simpson, '14, p. 848). 



This is a species which generally avoids smaller streams, both 

 in the Ohio and upper Tennessee drainages. Consequently, not 

 much difference is observed in obesity. Nevertheless a slight indi- 

 cation of our law is seen in so far, as the most compressed indi- 

 viduals come from the most extreme stations in the upstream 

 direction. 



Generally speaking, in the Ohio and Tennessee systems, this 

 species has a diameter between 50 and 70 per cent. Specimens fall- 

 ing under 50 per cent, are at hand from the following localities. 

 Licking Riv., Farmer. — Four specimens, dia. 47-45 per cent., aver- 

 age : 46 per cent. 

 Big Sandy Riv., Prestonsbiirg. — One among three specimens has the 



dia. of 44 per cent., the others have 50 and 52 per cent. 

 Pocatalico Riv., Raymond City. — Two specimens, dia. 48 and 45 



per cent. 

 Little Kanawha Riv., BurnsvUle. — One specimen wMth 46 per cent. 



(another with 50 per cent.). 

 Allegheny Riv., Kelly. — One specimen with 49 per cent, among 



others more obese. 

 Cheat Riv., Cheat Haven. — One specimen with 48 per cent., and 



two others more obese. 



All these stations are well upstream, and in no case, this species 

 has been found above these points. Thus it is seen, that unusually 

 flattened individuals turn up only in smaller streams or at the upper- 

 most limit of the distribution. In the Tennessee system, no speci- 

 mens under 50 per cent in diameter have been found. 



QuADRULA METANEVRA (Rafinesque) , and var. ward: (Lea). 

 Simpson, '14, pp. 834, 835. 



The form zvardi has been separated from typical mctanevra 

 because of its greater compression and greater smoothness, the large 

 knobs, so characteristic for the main species, being absent or very 

 slightly developed. 



