286 ORTMANN— CORRELATION OF SHAPE AND 



intervenes from which no shells are at hand, and that above Offutt 

 the Powell flows into the Clinch, the latter thus suddenly decreasing 

 in size. 



Material from the Powell is scanty, but it fits into the scheme. 

 It is thus clear that also the ciincolus-group is subject to the law. 

 It also holds good, as far as my material goes, in the Tennessee and 

 its tributaries in northern Alabama, where this type of shells also 

 seems to be abundant. 



Group of Fusconaia eugariana in the Upper Tennessee-system. 

 I distinguish the following two forms, but use the specific name 

 of cdgariana (see F. cor, Ortmann, 'i8, pp. 532, 533). 



1. Fusconaia edgariana (Lea). — Dia. 50 per cent, or over. 

 Unio edgarianiis Lea, '40 (Holston R., Tenn. ; Tennessee R., Flor- 

 ence, Ala.).- — Pleurohema edgariannm Simpson, '14, p. 741. 

 Dia. (Lea) : 64 per cent. ; (Simpson) : 58, 69, 76 per cent. 



Unio ohuncus Lea, '71 (Tuscumbia, Ala.; Holston R., Tenn.). — 



Synonym to cdgarianum, according to Simpson. 



Dia. (Lea) : 53 per cent. 

 Unio andersonensis Lea. '72 (Holston R. ; Clinch R., Anderson Co., 



Tenn.). — Synonym to cdgarianum, according to Simpson. 



Dia. (Lea) : 76 per cent. 



2. Fusconaia edgariana analoga (Ortmann). — Dia. less than 

 50 per cent. 



Fusconaia cor analoga Ortmann, '18, p. 533 (Chnch R., Speers 



Ferry). 



My material from Clinch River has furnished the. following 

 figures. 



Loc. No. Max. Min. Av. 

 Clinch River. 



Edgemoor i 58 58 58 cdgar. 



Needham Ford 2 51 42 46.5 anal, {cdgar.) 



Clinch River Station 2 48 47 47-5 anal. 



Sneedville i 49 49 49 anal 



Church Ford i 42 42 42 anal. 



Speers Ferry 8 49 43 46 anal. 



Clinchport 6 45 41 43 anal. 



St. Paul 7 45 40 43 anal. 



Fink 2 48 41 45 anal. 



Cleveland 6 44 40 42 anal. 



