58 MEMOIRS OF THE CARNEGIE MUSEUM. 



Interdentum well-developed and extremely wide. Lateral teeth short and strong. 

 Beak-cavity very deep, compressed. Dorsal muscle-scars on the hinge-plate. 

 Nacre of a peculiar and characteristic brownish purple color, lighter or darker, 

 sometimes shading to whitish toward the beak-cavity, and coppery-brownish, 

 iridescent posteriorly. 



Sexes absolutely indistinguishable in the shell. 



L. H. D. 



Size: 1. Godfrey, Cat. No. 61.4411 108 mm. 96 mm. 47 mm. 



2. Neville Island, Cat. No. 61.1637 77 " 73 " 41 " 



3. Utica, Cat. No. 61.3947 58 " 55 " 36 " 



Soft parts (See Ortmann, 1912, p. 258, fig. 7). Gravid females have been 

 found subsequently. Only the outer gills are charged, the placentae are sub- 

 cylindrical and white. Glochidia described and figured by Utterback (1916, PL I, 

 fig. 4). They are unusually large, 0.267 X 0.325 mm. Surber (1912, PL 2, fig. 19) 

 figures the glochidia of the closely allied R. granifera (Lea). These also are remark- 

 able for their size, 0.29 X 0.355 mm., but I have found them in R. granifera from 

 Black River, Arkansas, to be considerably smaller, 0.25 X 0.28 mm. 



Breeding season: I found my gravid females on May 22, 1914; May 25, 1915; 

 July 5, 1913; July 7, 1913; July 13, 1913. Utterback's glochidia were found on 

 August 11. 



Remarks: Although this species resembles in shape and sculpture several 

 other species, chiefly Quadrula pustulosa and Plethobasus cooperianus, it is always 

 easily recognized by the peculiar color of the nacre and the extremely broad inter- 

 dentum. I have old specimens, which are so much corroded at the beaks, that 

 the whole section bearing tubercles is gone, and only the smooth lower half of the 

 shell remains intact, yet the interior of the shell characterizes them. All Penn- 

 sylvanian specimens are rather flat, but farther down the Ohio occasional specimens 

 are met with which are somewhat more swollen. A specimen from Portsmouth, 

 Ohio, has distinctly more prominent and more incurved beaks, and might fall 

 under R. granifera (Lea) : but the other characters of the latter, as given by Simpson 

 (1900, p. 795, footnote 2) are absent. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Oliio River, Cooks Ferry and Industry, Beaver Co.; Neville Island, Allegheny Co. 



Beaver River, Wampum, Lawrence Co. (G. H. Clapp & H. H. Smith). 



Slipperyrock Creek, Wurtemberg, Lawrence Co. 



Allegheny River, Godfrey, Johnetta, and Kelly, Armstrong Co.; Walnut Bend, Venango Co. 



French Creek, Utica, Venango Co. 



Dunkard Creek, Wiley, Greene Co. 



Cheat River, Cheat Haven, Fayette Co. 



