296 ORTMANN— CORRELATION OF SHAPE AND 



North Fork Hoist on River. 



Rotherwood i 40 40 40 conr. 



Hilton 2 42 41 41.5 conr. 



Mendota 8 45 36 40 conr. 



Saltville 8 40 36 37 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. 



New Hope 10 64 49 57 dolab. ( conr. ) 



Paint Rock 10 57 38 45 conr. {dolab.) 



Princeton 7 44 38 40 conr. 



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. 



Group 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, 

 PI. cordatum- catillits and PI. cordatum coccineum, 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 cordatns (Rafinesque), and not obliquum 

 (Lamarck) : the reason for so doing will be given elsewhere). 



I. Pleurobema cordatum catillus "(Conrad). — Dia. 50 per 

 cent, or over. 

 Unio catillus Conrad, '36 (Scioto R., Ohio). 



Dia. (Conrad) : 51 per cent. 

 Unio solidus Lea, '38 (Ohio R., Cincinnati; Mahoning R., Ohio).— 



Quadrtila 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, '18, p. 547 ff. 



