<* 



114 MEMOIRS OF THE CARNEGIE MUSEUM. 



intergrades have not been observed, but may exist in the lower parts of the rivers. 

 Attention should be paid to this question. 



Localities represented in the Carnegie Museum: 



Mill-pond of Ratcliff Creek, Chestertown, Kent Co., Maryland (E. G. Vanatta). 

 Choptank Mills, Kent Co., Delaware (S. N. Rhoads). 



Localities represented in the Philadelphia Academy of Natural Sciences: 



Church Hill, Queen Anne Co., Maryland (E. G. Vanatta). 

 Potomac River, Washington, D. C. (G. W. Tryon, Jr.) (John Ford). 



Distribution and Ecology (See fig. 11): Type locality, Head of Chester River, 

 Maryland (Lea). 



Simpson reports this species from: "Virginia, Maryland, Pennsylvania," and 

 Rhoads (1904) from two localities in Delaware.''' There is no doubt that "Penn- 

 sylvania" is founded upon the records mentioned above (Gabb, and Hartman & 

 Michener). Gabb reports only a single specimen from his locality, the lower 

 Schuylkill River, and since this evidently offers the necessary conditions, there 

 is no reason to doubt the fact that the species has occurred there. However, I 

 entertain strong doubts that this species ever existed in White Clay Creek in Penn- 

 sylvania. I have been at White Clay Creek, at Avondale, Chester Co., Pennsyl- 

 vania, and here it is an upland stream, and does not at all present the conditions, 

 which I regard as being favorable for this species. It is possible that Hartman & 

 Michener found this species farther down in this creek, in the lowlands of the state 

 of Delaware, but not in Pennsylvania.''^ 



The evidence for the existence of this species in Pennsylvania rests upon the 

 single individual reported by Gabb. It is not impossible that it may be found 

 again, and the chance to rediscover it will be in or near the estuary of the Dela- 

 ware, for according to the records at hand this species seems to prefer the Coastal 

 Plain, living in slowly running rivers, ponds, or similar stations; it is a lowland 

 form, as I have pointed out elsewhere (Ortmann, 1913a, p. 361). 



Subfamily ANODONTIN.E (Swainson) Ortmann (1910). 

 Ortmann, 1910, p. 117; 19116, p. 336; 1912, p. 224. 



Key to the Genera of the AN0DONTiN.f;. 

 Oi. Beak-sculpture double-looped, with a sharp reentering angle or a sinuation. Mantle connection 

 between anal and supra-anal openings moderate or very long. No tendency to unite the 

 inner lamina of the inner gills with abdominal sac. 



"^ In addition to the above locality: Seaford, Sussex Co., Delaware. 



" The Carnegie Museum acquired in the Hartman collection a single set of this species, but there 

 is no indication that it came from our state, 



