200 Annals of the Carnegie Museum. 



Both forms, obliqiia (Lamarck) and pyramidata (Lea), are repre- 

 sented, and some individuals approach plena (Lea). They all pass 

 gradually into each other. In fact the intergrading forms are more 

 frequent than typical specimens, so that it is absolutely impossible to 

 draw the line between these supposed species. A more detailed ac- 

 count of the various forms constituting this very variable species will 

 be given elsewhere. 



44. Quadrula coccinea (Conrad). 



The type locality for this species is the " Mahoning River near 

 Pittsburgh" (Conrad). It is present in the Mahoning River at 

 Mahoningtown, Lawrence County. It does not occur in Harn's list, 

 although present in the upper Loyalhanna in Westmoreland County, 

 and it is not recorded by Stupakoff and Clapp. Rhoads has it from 

 the Beaver River at Wampum, Lawrence County. Specimens from 

 this locality are in the Carnegie Museum, collected by Clapp and 

 Smith. 



It is generally distributed in the Beaver drainage in Lawrence and 

 Mercer Counties. It is found in Buffalo Creek, Butler County ; in 

 Little Mahoning Creek, Indiana County ; in the French Creek drain- 

 age in Venango, Crawford, and Erie Counties ; in Brokenstraw Creek 

 in Warren County ; and in the upper Allegheny in McKean County. 

 In the Allegheny River from Armstrong to Warren Counties, there is 

 a form, which inclines both toward typical Q. obliqua, and the form 

 pyramidata. In the southwestern portion of the state (Monongahela 

 drainage) this species seems to be absent. 



This species does not belong to the genus Quadrula. At the breed- 

 ing season, the outer gills only are used as marsupia, and thus it should 

 be placed, according to Simpson's arrangement of the genera, with 

 the genus Pleurobevia. I possess a number of gravid females from 

 Neshannock Creek in Lawrence County, and from the upper Alle- 

 gheny in McKean Country. 



45. Quadrula subrotunda (Lea). 



Cited by Harn from western Pennsylvania. The U. pilaris of 

 Clapp (Allegheny County) and of Rhoads (Coraopolis) are probably 

 this form. The majority of Rhoads' ohliquus (Coraopolis and Beaver) 

 belong here. 



It is abundant in the larger rivers : Ohio, Monongahela, and Alle- 

 gheny. In the Monongahela it extends up to the Cheat River in 

 Fayette County, in the Allegheny up to the northern part of Arm- 

 strong County. 



