188 



MEMOIRS OP THE CARNEGIE MUSEUM. 



Otherwise this form is Uke the western marginata, and differs markedly from 

 the common eastern A. varicosa, with which it is sometimes foimd associated. 



L. 



H. 



Size: 1. Carlisle, Cat. No. 61.4677 (9 gravid) ... .79 mm. 41 mm. 30 mm. 



2. do. " " do. (c?) 71 



3. do. " " do. ( 9 gravid) 69 



4. Selinsgrove, Cat. No. 61.4679 (9 gravid) .66 



5. do. " " do. (cf) 61 



6. do. " " do. (cf) 47 



Soft parts and glocMdia identical with those of A. marginata. 



Breeding season: The following records for gravid females are at hand: Aug. 

 13, 1908; Aug. 13, 1910; Aug. 14, 1910; Aug. 20, 1909; Aug. 20, 1909; Aug. 21, 

 1909; Sept. 8, 1909. 



These dates indicate only the begimiing of the breeding season early in August 

 (eggs and glochidia found on first date!). Thus it is probably bradj^tictic. 



Remarks: This is a new form, which has not been distinguished previously. 

 It comes very near to the western A. marginata in shape, having a rather sharp 

 posterior ridge and a more or less distinctly truncated posterior slope, and having 

 the beaks nearer to the middle of the shell (at about one third of the length of 

 the shell) . It is practically a marginata in shape with a peculiar color, and is thus 

 more closely allied to the western shell than to the eastern A. varicosa, and its 

 presence on the Atlantic side is highl}^ interesting. 



Wherever this form is found associated with the eastern varicosa, the two may 

 be distinguished at a glance, varicosa being smaller, with posterior ridge and pos- 

 terior truncation less developed, and with generally a darker epidermis, without 

 distinct spots, and the posterior slope not lighter, but rather darker than the rest 

 of the shell. 



Localities represented in the Carnegie Museum: 



Susquehanna River, Duncannon, Perry Co., Pennsylvania. 



Susquehanna River, Selinsgrove, Snyder Co., Pennsylvania. 



Conodoguinet Creek, Carlisle, Cumberland Co., Pennsylvania. 



Juniata River, Juniata Bridge, Perry Co., Pennsylvania. 



Frankstown Branch Juniata River, Huntingdon and Ale.xandria, Huntingdon Co., Pennsylvania. 



(D. A. Atkinson). 

 Raystown Branch Juniata River, Ardenheim, Huntingdon Co.; and Mount Dallas, Bedford Co., Penn. 



sylvania. 

 Penns Creek, Selinsgrove, Snyder Co., Pennsylvania. 

 North Branch Susquehanna River, Tunkhannock, Wyoming Co., Pennsylvania. 



