UPPER TENNESSEE DRAINAGE. 551 
resemble very much in this the P. clava, although some peculiar 
variations are observed in the color of certain parts. 
As it happens, the oldest name (oviforme) has been used for an 
intermediate form, and thus, in order to retain this in its original 
sense, it seems advisable to distinguish three types within this 
species: the headwaters form (argenteum) has a diameter of less 
than 40 per cent. of the length; the form of the medium sized rivers 
(oviforme) has a diameter from 40 to 49 per cent.; and the big 
river form (holstonense) has 50 per cent and over. 
Also here we see the phenomenon that the headwaters form gains 
in circumference what it has lost in obesity. The argenteum type 
shows this possibly to the greatest extent; shells of this form reach 
in length and height dimensions entirely unknown in the more swol- 
len forms. 
30. PLEUROBEMA OVIFORME (Conrad), 1834. 
Unio oviformis Conrad, °34.—Unio ravenelianus Lea, ’34.—Unio 
patulus Conrad, ’38 (not patulus Lea, ’29)—Unio lesleyi Lea, 
’60.—Unio ornatus Lea, ’61.—Unio clinchensis Lea, ’67——Unio 
conasaugaensis Lea, ’72—Unio clinchensis, lesleyi, patulus Lewis, 
'71.—Pleurobema oviforme Goodrich, ’13, p. 94.—Pleurobema 
clinchense, lesleyi, oviforme, ornatum, conasaugaense, raveneli- 
anum Simpson, ’14, pp. 743-800. 
This resembles much the upper Ohio form of P. clava, but is less 
cuneate, with the beaks less anterior. It is extremely variable in 
shape, higher or more elongate, and the color pattern is hardly ever 
alike in any two individuals. 
In the Walker collection are topotypes of U. ravenelianus Lea 
(from Asheville): six specimens have the diameter of oviforme 
(40-49 per cent., while one has the diameter of 38 per cent. and the 
latter would thus fall under argenteum. But it has the typical shape 
of oviforme. Since the type of ravenelianus has 43 per cent., accord- 
ing to Simpson, we should place this here, and these shells are, 
indeed, nothing but oviforme without rays, of a general dull color 
(pale ‘brownish, not yellowish). Such specimens are found else- 
where, and several sets in the Walker collection, from Poplar Creek, 
