STATION IN FRESH-WATER MUSSELS. 305 



prevail at the upper stations. The metropolis of caperatus is clearly 

 in Clinch and Powell Rivers, toward the headwaters. It should be 

 noticed that this species does not go very far up in the rivers, and 

 that it is by no means a small-creek-form. 



Group of Obovaria subrotunda in the Upper Ohio-drainage. 



The synonymy of these forms is as follows (see Ortmann, 'i8, 

 p. 567, 568, but the name lens has been restored for Icvigata). 



1. Obovaria subrotunda (Rafinesque). — Dia. 60 per cent, or 

 over. 



Ohliquaria subrotunda Rafinesque, '20 (Ohio). — Obovaria subro- 

 tunda Vanatta, '15, p. 552. 

 Dia. (Vanatta) : 72 per cent. 



Unio circulus Lea, '29 (Ohio R., Cincinnati; Monongahela R., Pitts- 

 burgh). — Obovaria circ. Simpson, '14. p. 291. 

 Dia. (Lea) : 73 per cent.; (Simpson) : 58, 67, 72 per cent, (the 



first given by Simpson falls under the variety !). 



2. Obovaria subrotunda lens (Lea). — Dia. less than 60 per cent. 

 Unio lens Lea, '31 (Ohio and Tennessee). — Obovaria lens Simp- 

 son, '14, p. 293. 



Dia. (Lea) : 48 per cent.; (Simpson) : 52 per cent. 



The material from the upper Ohio system shows that these two 

 forms intergrade completely, as I have pointed out already in 1909, 

 and subrotunda is the large-river-form, while lens is found toward 

 the headwaters. 



Loc. No. Max. Min. Av. 



Ohio River. 



Portland 12 66 53 62 suhr. {lens) 



Parkersburg 2 62 59 60.5 sitbr. {lens) 



St. Mary's 7 67 51 62 subr. {lens) 



CoraopoHs 5 64 57 61 subr. {lens) 



Monongahela River. 

 Charleroi 5 68 53 60 subr. {lens) 



West Fork River. 



Lynch Mines 4 56 50 53 lens 



Lightburn 3 49 48 49 lens 



Weston 2 49 45 47 lens 



