294 ORTMANN— CORRELATION OF SHAPE AND 



fera) of the lower parts of the river passes gradually into the more 

 compressed form {inhere iilata) of the headwaters, I have not suffi- 

 cient material to substantiate this by measurements, since all my 

 material, from the middle Ohio upwards, and from the upper Ten- 

 nessee, clearly belongs to the compressed tuberetdata^type. But the 

 general rule, at least, is thus confirmed, that the swollen form, 

 granifera, is not found in the upper course of these rivers. 



Group of Lexingtonia dolabelloides in the Upper Tennessee- 

 system. 



The dolabelloides-group is common in the upper Tennessee, and 

 also in the Tennessee-drainage in Alabama, and I again distinguish 

 a swollen and a compressed form, the first in the larger rivers, the 

 second in the headwaters. They pass gradually into each other, 

 and the line drawn between them, at the diameter of 50 per cent., 

 again is artificial. The nomenclature and synonymy is as follows :^^ 



I. Lexington dolabelloides (Lea). — Dia. 50 per cent, or over. 

 Unio dolabelloides Lea, '40 (Holston R., Tenn.). — Pleurobema del. 



Simpson, '14, p. 752. 



Dia. (Lea) : 63 per cent. ; (Simpson) : 6y and 71 per cent. 

 Unio thorntoni Lea, '57 (Tuscumbia, Ala.). — Recognized as syn- 

 onym by Simpson. 



Dia. (Lea) : 66 per cent. 

 Unio mooresianns Lea, '57 (Tuscumbia, Ala.). — Synonym, accord- 

 ing to Simpson. 



Dia. (Lea) : 67 per cent. 

 Unio recurvatus Lea, '71 (Tennessee R. ; Holston R.). — Synonym, 



according to Simpson. 



Dia. (Lea) : 63 per cent. 

 Uino circumactus Lea, '71 (Florence, Ala.; Holston R., Tenn.). — 



Synonym, according to Simpson. 



Dia. (Lea) : 58 per cent. 

 Unio subglobaUis Lea, '71 (Florence, Ala.; Nashville, Tenn.). — 



Synonym, according to Simpson. 



Dia. (Lea) : 73 per cent. 



19 See Ortmann, Proc. Amcr. Philos. Soc, 57, '18, pp. 545, 546. 



