302 ORTMANN— CORRELATION OF SHAPE AND 



There are some irregularities in the CHiich, which may be ex- 

 plained by insufficient matrial. The form oviforme goes up to the 

 uppermost locality, but it becomes rare in the headwaters ; and 

 further, it may give way entirely to argentemn above Cedar Blufif. 

 The decease of obesity is noted chiefly in the minima. 



In Pozvell River, oinfonne alone or associated with argenteum 

 goes up to dinger. However, at Big Stone Gap, among 9 speci- 

 mens, the max. was 38 per cent., the min. 31 per cent., and the av. 

 35 per cent. : pure argenteum. 



The same law is observed in other tributaries of the Tennessee 

 system in East Tennessee. In French Broad River at Boyd Creek, 

 oviforme prevails, with occasional holstonensc. In the mountains 

 at Asheville, the average diameter was found to be 44 per cent. 

 (oviforme), with occasional argenteum among them. I have ex- 

 amined 6 specimens in the Walker collection, labeled ravenelianum, 

 with the max. of 49 per cent, and the min. of 38 per cent. A very 

 similar form I collected in Hiwassee River at Austral ; in 8 speci- 

 mens the max. was 52 per cent., the min. 43 per cent., and the av. 

 48 per cent. : these represent oviforme with occasional Jiolstonense. 



Also in northern Alabama and the adjoining parts of Tennessee 

 I have found evidence for our law, as is shown by the following 

 instances. 



Loc. No. Max. Min. Av. 



Paint Rock River. 



Paint Rock 2 55 50 52.5 hoist. 



Trenton 2 41 41 41 ovif. 



Princeton 5 47 39 42 ovif. {argent. ) 



Elk River. 



Fayetteville i 44 44 44 ovif. 



Estill Springs 8 41 2,2, 36 argent, {ovif .) 



Boiling River, Cowan 4 42 36 38 argent, (ovif.) 



The last two localities are about equivalent as to their situation. 



Group of Pleurobema clava. 



Pleurobema clava is absent in the upper Tennessee-region. It 

 turns up, however, in the Tennessee drainage in northern Alabama. 

 Yet my material is too scanty to form an opinion as to the interrela- 

 tion of this form with oviforme. PI. clava is abundant in the upper 



