70 MEMOIRS OF THE CARNEGIE MUSEUM. 



Clapp, 1895 (Allegheny Co.). 



Rhoads, 1899 (Ohio River, Coraopolis, Allegheny Co.)." 



Ortmann, 19096, p. 199. 



Characters of the shell: Shell rather large, heavy. Outline subtriangular, 

 rounded before, subangular and more or less drawn out at the lower posterior end, 

 with the lower margin gently convex in the anterior part, and generally concave in 

 the posterior part, and with the supero-posterior margin gently curved. Beak 

 more or less elevated, and swollen, directed obliquely forward, or more or less 

 incurved, situated nearer to the anterior end of the shell. Beak-sculpture rudi- 

 mentary, consisting of two or three indistinct, concentric bars. Shell rather swollen 

 anteriorly, the diameter generally over fifty percent of the length. Posteriorly 

 the shell is compressed, with a broad, more or less distinct, radial furrow, running 

 from the beaks toward the lower posterior margin, producing there a shallow 

 emargination. Surface of shell smooth, without any sculpture. Behind the radial 

 depression there is a rounded, low elevation, which, however, does not form a dis- 

 tinct ridge, and passes insensibly into the posterior slope. 



Epidermis lighter or darker brown, generally of a dark chestnut hue, blackish, 

 when old, with fine and indistinct green or blackish capillary rays, or bundles of 

 rays, which are mostly entirely obliterated in old specimens. The rays do not 

 break up into blotches. Growth-rests more *or less distinct, darker than the rest 

 of the shell. 



Hinge-teeth well-developed, rather strong. Pseudocardinals divergent, ragged. 

 Interdentum rather wide. Lateral teeth moderately long. Beak-cavity more or 

 less deep, often somewhat compressed. Dorsal muscle-scars on the hinge-plate. 

 Nacre mostly white, rarely reddish. 



No sexual differences in the shell. 



L. H. D. Pr.ct. 



Size: 1. Industry, Cat. No. 01.3900 (unusually 



produced) 109 mm. 82 mm. 46 mm. .42 



2. Industry, Cat. No. 61.3902 90 " 77 " 51 " .57 



3. Godfrey, Cat. No. 61.39010 83 " 69 " 42 " .51 



4. Charleroi, Cat. No. 61.2869 59 " 52 " 33 " .56 



Soft parts (See Ortmann, 1912, p. 264). I have examined nearly a thousand 

 individuals of this species, and have found the structure of the soft parts as de- 

 scribed, with only the outer gills marsupial. However, a few exceptions have 

 been noted in the case of five specimens received through the courtesj' of Dr. R. 



" As has been stated by the writer (1909&, pp. 186 and 199) only part of the specimens from Cora- 

 opolis, recorded by Rhoads, belong to PI. ohliqxium, the rest are Fusconaia suhrotunda, while all of Rhoads' 

 specimens from Beaver (in the Philadelphia Academj') are F. suhrotunda. 



