UPPER TENNESSEE DRAINAGE. 551 



resemble very much in this the P. clava, ahhough some pecuhar 

 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 (argenteiim) 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 (holstoneiise) 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 argenteiim 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. 



Uiiio oviformis Conrad, '34. — Unio ravenelianiis Lea, '34. — Unio 

 patulus Conrad, '38 (not patiilits Lea, '29). — Unio lesleyi Lea, 

 '60. — Unio ornatus Lea, '61. — Unio clinchensis Lea, '67. — Unio 

 conasangaensis Lea, ''/2.—Unio clinchensis, lesleyi, patulus Lewis, 

 '71. — Pleurobcma oviforme Goodrich, '13, p. 94. — Pleurohema 

 clinchense, lesleyi, oviforme, ornatnm, conasaugaense, ravencli- 

 annm 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 oi 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, 



