290 ORTMANN— CORRELATION OF SHAPE AND 



mixture of some specimens of barnesiana. From Sevierville, I have 

 ten specimens, ranging from 45 to 38 per cent., the average being 

 42 per cent., thus representing barnesiana with an interspersing of a 

 few bigbycnsis. I have no doubt, however, that, if there was any 

 material from farther up stream, pure bigbyensis would appear. 



Finally, the same conditions obtain in the Tennessee drainage in 

 northern Alabama. In the Tennessee River at Florence is a form 



• 



(12 specimens measured) in which the diameter ranges from 64 to 

 50 per cent., with the average at 56 per cent. This is pure tumes- 

 ceiis. In the tributaries we find mostly the more compressed forms 

 of the barnesiana- and bigbyensis-type, so, for instance, in Elk 

 River, at Fayetteville (i specimen), a form with the diameter of 

 44 per cent, (barnesiana), and farther up, at Estill Springs (8 

 specimens), a form ranging from 40 to 35 per cent., with the average 

 of 38 per cent., which corresponds to bigbyensis. 



Thus the contention is substantiated, that tuvnescens of the large 

 rivers passes through barnesiana into bigbyensis of the headwaters. 



Group of Amblema peruviana (Lamarck). 



The extremes of this group of forms are marked by Amblema 

 peruviana (Lam.) (= Quadrula plicata Simpson, '14, p. 814) and 

 Amblema costata (Raf.) (= Quadrula undidata (Barn.) Simpson, 

 p. 819). But there are other described "species" which fall into 

 this group. 



Wilson and Clark (1914) and Utterback (1916) have referred to 

 these as showing the same phenomenon of a swollen form inhabit- 

 ing the large rivers, and a flat one in the smaller streams (Cumber- 

 land and Osage River systems). I have no doubt that this is 

 correct, and that it applies also to other rivers. 



According to my experience, there is no question that specimens 

 of A. costata in the Ohio River below Pittsburgh are more obese 

 than the greatly compressed specimens found, for instance, in the 

 Beaver and upper Allegheny drainages. However, I do not possess 

 sufficient material from the middle and lower Ohio, to show the 

 actual transition into peruviana. Also in the Tennessee-system, I 

 did not go far enough down to reach the range of the latter : what I 



