302 ORTMANN—CORRELATION OF SHAPE AND 
There are some irregularities in the Clinch, 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 argenteum above Cedar Bluff. 
The decease of obesity is noted chiefly in the minima. 
In Powell River, oviforme alone or associated with argenteum 
goes up to Olinger. 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 holstonense. In the mountains 
at Asheville, the average diameter was found to be 44 per cent. 
(oviforme), with occasional argentewm 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 holstonense. 
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. 
Pantit? WO Chee-c ap enctsies tevae ieee ohstes 2 55 50 52.5 holst. 
BSE Giahdoloe ea Oe Gio ACAI Re AS 2 4I 4I 4! ovif. 
PiIICEtOMs «nee roee seep tes eee ee 5 47 390 42 ovif. (argent. ) 
Elk River. 
Bavettevillet ear scr tates minis oer I 44 44 44 ovif. 
Bist Spritiese, sveeeccacicne oe 8 41 83 36 argent. (ovif.) 
Bothng River, Cowan .....-0... 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 
