STATION IN FRESH-WATER MUSSELS. 293 
large knobs, but also the nodules.” It hardly, however, forms a 
distinct race here, being rare, and passing insensibly into the normal 
type. 
In the upper Tennessee; there is an analogous form, also greatly 
compressed, and without the large knobs. It is, however, not 
smooth, but thickly covered with small nodules, even more so than 
the normal form. It has been called var. strigillata (Wright). 
‘absolute 
‘ 
Simpson (1. c.) does not accept this, because there is an 
graduation” to this form. Yet in the upper Clinch, from the Ten- 
nessee-Virginia state line upward, this variety becomes a pure race, 
which is very striking. It is also in Powell River and the North 
Fork Holston, but not so well developed. 
In this instance, it is clearly seen that analogous, compressed 
forms are being developed independently in the upper Ohio and the 
upper Tennessee systems, and their independence is shown by the 
difference in the character of the nodules: the one is practically 
smooth, the other strongly nodulous. But in the disappearance of 
the large knobs they agree again. 
I shall give here the measurements of the form in the Clinch 
River. In the last column, in this case, the name given refers to the 
development of the large knobs. 
Loc. No. Max. Min. Av. 
I OTT OO Sunes ater severe) vere Brey enenctenel cls ates 3 35 34 35 cyl. 
Ginny Pees socveractarers ta ators os 2 41 31 39 cyl. 
ClinchwiRiver Statront syeemeenee 6 30 34 36 cyl. 
Speers) Herny, boca ead ws ad onate 2 38 34 36 cv. 
@linch port Sokattectoe seetitvew ees ccs: 5 35 32 33 cyl. (strig.) 
uitaleons Ohara <class ciara sk wots GOS a4, Sa ast cyl.-strig. 
Cleveland \ seen itac ctrdse te ade oes 6 35 28 31 strig. 
IReagvie titans ceettetsn sees Sraftrorel ian eierei nae slsih ore 2 30 30 30 strig. 
Ratchvlanrdieer ee ttees sper cokes doie aoc 4 31 28 30 strig. 
(Cocke. jaithit” 2 mea ee memeber odes I 27 7) 27 strig. 
ROTUNDARIA TUBERCULATA (Rafinesque), and R. GRANIFERA (Lea). 
Quadrula tub. and gran. Simpson, ’14, pp. 903, 905. 
According to Wilson and Clark,** these two forms show, in the 
Cumberland River, the phenomenon that the swollen form (grani- 
17 Sterki, Pr. Ohio Ac., 4, 07, p. 390, mentions this form first. 
USE Cal Abap 03% 
PROC. AMER. PHIL. SOC., VOL. LIX, S, AUGUST 20, 1920. 
