178 MEMOIRS OF THE CARNEGIE MUSEUM. 



Hinge incomplete. Pseudocardinals present, stumpy, crenulated, generally 

 one in right, two in left valve, of which the anterior may be rudimentary. Inter- 

 dental tooth of left valve poorly developed, generally connected with the posterior 

 pseudocardinal. Laterals practically absent. Beak-cavity moderately . deep. 

 Dorsal muscle-scars distinct, upon the hinge-plate. Adductor scars deeply im- 

 pressed anteriorly, less so posteriorly. Nacre white, salmon, pink, or red, the red 

 shades prevailing, very iridescent posteriorly. 



Shell of male and female indistinguishable. 



L. H. D. 



Size: 1. Kmberton Dam, Cat. No. 61.883 77 mm. 52 mm. 37 mm. 



2. Tioga, Cat. No. 61.4242 ( 9 gravid) 69 " 41 " 28 " 



3. do. " " do. id") 56 " 34 " 23 " 



4. Greencastle, Cat. No. 61.4247 (9 gravid) 48 " 32 " 18 " 



5. do. " " do. (cf) 42 " 27 " 16 " 



Soft parts (See Ortmann, 1912, p. 296). Glochidia (See Ortmann, 19116, 

 PI. 89, fig. 9). 



Breeding season: I have the following dates for gravid females: July 18, 

 1908; July 22, 1910; Aug. 10, 1910; Aug. 11, 1910; Aug. 12, 1908; Aug. 13, 

 1910; Aug. 19, 1909; Sept. 5, 1909; Sept. 6, 1909. Then in spring, April 24, 

 1909; April 26, 1909; May 6, 1912; May 10, 1912; May 11, 1912; June 7, 1912; 

 June 12, 1912; June 14, 1910. 



This is clearly a bradytictic form, with a rather short interim, in June and July. 



Remarks: Quite a well characterized species, not to be confounded with any 

 other Pennsylvanian form, and having no related forms in the interior drainage 

 system. The most nearly allied species are found in the southern parts of the 

 Atlantic watershed, South Carolina and Georgia. It is easily recognized by the 

 shape of the shell, heavy beak-sculpture, by the color and markings of its epi- 

 dermis, and, on the inside of the shell, by the peculiar character of the hinge, 

 and the often beautifully red tints of the nacre. 



It is a rather variable shell, and the chief variations have been alluded to 

 above. 



Pennsylvanian localities, represented in the Carnegie Museum: 



Delaware-drainage : 

 Delaware River, Yardley, Bucks Co.; Shawnee, Monroe Co. 

 White Clay Creek, Avondale, Chester Co. 

 Schuylkill Canal, Manayunk, Philadelphia Co. 

 Kimberton Dam, Chester Co. (Hartman collection) (formed by French Creek, near Phoenixville, Chester 



Co.) 

 Princess Creek, Kunkletown, Monroe Co. 



