STATION IN FRESH-WATER MUSSELS. 289 
It hardly needs to be pointed out that, beginning in the large 
rivers, tumescens 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. Min. Av. 
Clinch River. 
So lwalyasctten oe ie alec otra cisshetts I 38 38 38 bigb. 
TekalexeanVGYOIr’ Y sic pune pons o Come aon 4 2 49 50 tum. (barn.) 
Gltnitone cen, Aeros oa ose ceo I 45 45 45 barn. 
IW ial etal ond i. cevcsvers cess otctier elev rs 2 4Q 46 47.5 barn. 
Kevlem Eo ncn scuhetnte cree oemin ce I 4I 41 4I barn. 
Clinchponte eerie en eee I 36 36 36 bigb. 
Stee battle cone ermesicei secre cierto de I 35 35 35 bigb. 
BiimikaMa en ce masta ccievola ie mateo e I 38 38 38 bigb. 
TCAVICHI Dear turnin toate shiavpoeres ease 6 38 2 30 bigb. 
Rachilamcdey vie seae cremate yeroeintts oie 12 40 33 36 bigb. (barn.) 
Cedar Bitte sacucee a asiecise acetae 10 30 2 36 bigb. 
saz ewe mite acer vo siecveiieresstee arn I 30 39 39 bigb. 
Powell River (next station below is Clinton, with 45 per cent. = barn.). 
Loc. No. Max. Min. Av. 
Greens ahord tcc. scone see es 2 40 40 40 barn. 
(SOmD Same et AR ick ei as 4 37 36 37 bigb. 
RO SemetNEA eave wera tac tere sicrane I 37 37 37 bigb. 
Wry. clenlgmcn ices cone ee iio ees 7 41 36 39 bigb. (barn.) 
BiowStonenGapy eo anscatocinceiiccn: 12 41 BT 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- 
