86 MEMOIRS OF THE CARNEGIE MUSEUM. 



Tennessee-drainage: 

 Tennessee River, Knoxville, Knox Co., Tennessee. 

 French Broad River, Boyd Creek, Sevier Co., Tennessee. 

 Holston River, McMUlan and Mascot, Knox Co.; Hodges, Jefferson Co.; Turley Mill, Nocton, and 



Holston Station, Grainger Co.; Austin Mill, Hawkins Co., Tennessee. 

 Clinch River, Solway, Knox Co.; Edgemoor and Offutt, Anderson Co.; Needhams Ford (B. Walker, 



donor) and Black Fox Ford, Union Co.; Clinch River Station, Claiborne Co.; Oakman, Grainger 



Co., Tennessee. 



There are a good many specimens at liand from west of the Mississippi, from Arkansas, Kansas, 

 and Oklahoma, but since these form a peculiar and rather obscure association of forms, partly intergrading 

 with the var. catillus, partly having characters of their own, I omit them here, till further investigations 

 have been made. 



Distribution in Pennsylvania (See fig. 8) : 



The range of this form in Pennsylvania, is coextensive with that of P. obliquwn, 

 but it is rather rare. The same is true farther down the Ohio, and wherever I 

 collected it myself between Pittsburgh and Cincinnati I found only a few specimens 

 of it among large numbers of ohliquum and its intergrades. 



General distribution: Type locality, Kentucky River (Rafinesque). 



Where P. obliquum is found, this form generally is also present. However, 

 P. obliquum rubrum seems to have a wider range than the main form, for it is also 

 found west of the Mississippi without being associated with P. obliquum (See 

 above). I also have observed in the upper Tennessee-drainage, that it ascends 

 in the Holston and Clinch a little farther than the main species. 



Note: Attention should be called again to the fact, that we have here a group 

 of forms (obliquum-group) , of which some have swollen shells {obliquum and catillus), 

 which are found in the larger rivers, while another allied form has a compressed 

 shell {coccineum), which is peculiar to small creeks. As in certain other cases, 

 there is also a dwarfed lacustrine form, pauper culum. 



It is well to keep these facts in mind. My observations on the passing of the 

 creek form into that of the large rivers have been confirmed for the Kankakee- 

 drainage in Indiana and Illinois by Wilson & Clark (1912, p. 42). However, the 

 remark of these authors, that I am of the opinion that these forms are "identical" 

 rests upon a misunderstanding. They are "conspecific," and represent well 

 marked races, or varieties, of the same species, but they are not identical. 



Pleurobema clava (Lamarck) (1819). 

 Pleurobema clava (Lamarck) Simpson, 1914, p. 735. 



Plate VII, figs. 7, 8, 9. 

 Records from Pennsylvania: 



Call, 1SS5 (Allegheny River, as U. patulus). 

 Harn, 1891 (western Pennsylvania). 



