STATION IN FRESH-WATER MUSSELS. 281 
These tables do not need any further comment: barring certain 
local irregularities, which can be accounted for by scarcity of ma- 
terial, the law is clearly shown, that in the upstream direction the 
diameter decreases, and that it decreases very gradually. The con- 
ditions in the Holston, and chiefly in the Clinch and Powell are, 
indeed, classical. 
It should be added that I have seen a single individual from 
Little Tennessee River, Coytee, Loudon Co., Tenn., which has the 
diameter of 58 per cent. (= pilaris). Little Tennessee goes into 
the Tennessee below Knoxville, and thus this agrees well with the 
figure for specimens from Knoxville (57 per cent.). 
I further collected a large number of specimens in French Broad 
River, at Boyd Creek, Sevier Co., Tenn. This river unites with 
the Holston to form the Tennessee just above Knoxville. I have 
measured 16 specimens; the max. is 64 per cent.; the min. 47 per 
cent.; the av. 56 per cent. Also these figures are exactly what we 
should expect. 
There is no question that all these shells are one and the same 
species, for which the name filaris, as the oldest, should be used, 
and which changes in obesity from the large rivers towards the 
headwaters. Since Lea distinguished, at the same time, two forms 
which differ chiefly in being more or less swollen, the two names 
given by him (pilaris and lesueuriana) should be preserved in a 
varietal sense, and a third variety of great compression should be 
added, described much later by Wright as bursa-pastoris. 
As pilaris corresponds to subrotunda, bursa-pastoris corresponds 
to kirtlandiana of the upper Ohio drainage. In fact, it is so close to 
it that Pilsbry and Rhoads’? have identified specimens from Wa- 
tauga River as kirtlandiana. I have serious doubts that the two 
forms can be kept apart, when the locality is unknown. In my 
large material I can see only one difference, that is, that bursa- 
pastoris is a smaller shell than kirtlandiana, and reaches a greater 
degree of compression. This opens a very pertinent question as to 
nomenclature, since also pilaris (and Jesuewriana) apparently repre- 
sent only a small race of subrotunda. I shall not go any further 
12 Pr, Ac. Nat. Sct., Philad., 48, 1896, p. 502. 
