296 ORTMANN—CORRELATION OF SHAPE AND 
North Fork Holston River. 
Rothenw Oo daeercm cok actecei metros I 40 40 40 conr. 
tome. cece aero eure onic ees 2 2 41 41.5 conr. 
IMiem Cotas scr eters eee site neste ie 8 45 36 40 comr. 
Sallevilles Gass siocivernshe otasadeleectaers 8 40 36 ey/ conr. 
Finally, I am able to tabulate the conditions in Paint Rock River 
in Alabama. It should be remembered that, in the main river in 
this region, dolabelloides is present with the average dia. of 67 and 
60 per cent., and the minimum of 54 per cent. 
Loc. No. Max. Min. Av. 
INE Was LODE! firs sicelsrere atete inane. 10 64 49 57 dolab. (conr.) 
I AATUTNESO CIN epee sre cuctahpee ei eatans 10 57 38 45 conr. (dolab.) 
Rrincetonieesccstiatations serene cei 7 44 38 40 comr. 
This last series completely connects the two forms, which con- 
nection was not so evident in the lower Clinch on account of the 
scarcity of material. 
GrRouP OF PLEUROBEMA CORDATUM IN THE UPPER OHIO-DRAINAGE. 
This is an extremely difficult and polymorphous group on ac- 
count of the complexity of conditions and the variability of other 
characters of the shell, besides obesity. I have indicated, in a gen- 
eral way, the main phases of this species.*° But most of them may 
be dismissed for our present purposes. Yet there are two of them, 
Pl. cordatum catillus and Pl. cordatum ceccineum, which clearly 
submit to the law, as will be demonstrated in the tables. 
The synonymy of these forms is as follows (It should be noted 
that I call the main species cordatus (Rafinesque), and not obliquum 
(Lamarck) : the reason for so doing will be given elsewhere). 
I. PLEUROBEMA CORDATUM CATILLUS (Conrad).—Dia. 50 per 
Cent. .Or (OVEF. 
Unio catillus Conrad, ’36 (Scioto R., Ohio). 
Dia. (Conrad): 51 per cent. 
Unio solidus Lea, ’38 (Ohio R., Cincinnati; Mahoning R., Ohio).— 
Quadrula solida Simpson, ’14, p. 885. 
Dia. (Lea): 60 per cent. Of the four specimens measured by 
Simpson, only two belong here with the Dia. 58 and 59 per cent. 
20 Ortmann, 718, p. 547 ff. 
