STATION IN FRESH-WATER MUSSELS. 289 



It hardly needs to be pointed out that, beginning in the large 

 rivers, tumesccns passes gradually into barnesiana, and farther up, 

 into bigbyensis. This is one of the best and most convincing series. 



In Clinch River, conditions are similar, but the only specimen 

 from the lowermost station (Solway) makes an exception, but a 

 rather striking one. We may however, very well disregard it, and 

 take it simply for an abnormal case. With the next station above it 

 (Edgemoor), the normal condition is seen to begin. 



Loc. No. Max. JMin. Av. 

 Clinch River. 



Solway I 38 38 38 bigb. 



Edgemoor 4 52 49 50 turn, (barn.) 



Clinton i 45 45 45 bani. 



Walker Ford 2 49 46 47-5 barn. 



Kyle Ford i 41 4i 4i barn. 



Clinchport i 36 36 36 bigb. 



St. Paul I 35 35 35 bigb. 



Fink I 38 38 38 bigb. 



Raven 6 38 3^ 36 bigb. 



Richland 12 40 33 36 bigb. (barn.) 



Cedar Bluff 10 39 32 36 bigb. 



Tazewell ; i 39 39 39 bigb. 



Powell River (next station below is Clinton, with 45 per cent. = barn.). 



Loc. No. Max. Min. Av. 



Greens Ford 2 40 40 40 barn. 



Combs 4 37 36 37 bigb. 



Rose Hill I 37 37 37 bigb. 



Dryden 7 4i 36 39 bigb. (barn.) 



Big Stone Gap 12 41 31 36 bigb. (barn.) 



No comment is necessary, except that it should be noted that, in 

 this species, the intermediate form (barnesiana) turns up, occa- 

 sionally, way up in the headwaters. This, of course, is due to the 

 fact that the limits drawn between the three forms are very narrow. 



In some of the tributaries of the upper Tennessee, tumescens. 

 according to my material, passes only into barnesiana, without the 

 most compressed form of bigbyensis being well represented. This 

 is seen, for instance, in Little Pigeon River at Sevierville, a tribu- 

 tary to the French Broad. The latter, at Boyd Creek possesses 

 tumescens with the average diameter of 50 per cent., with an ad- 



