138 MEMOIRS OF THE CARNEGIE MUSEUM. 



Anodonta grandis Say (1829). 

 Anodonta grandis Say; Simpson, 1914, p. 418. 



Plate X, figs. 1, 2. 

 Records from Pennsylvania: "° 



Ortmann, 19096, p. 195. It is very remarkablp that this common species has never before been reported 

 from western Pennsylvania. 



Characters of the shell: Shell large, sometimes very large, but generally rather 

 fight and thm, often very thin. Outline subovate or subelliptical, more or less 

 elongate, rounded anteriorly, more or less narrowed behind, often somewhat 

 pointed. Lower margin more or less convex, upper margin straight, often forming 

 an angle with the obliquely descending posterior margin, which in manj' cases 

 forms a moderately developed wing, but in other cases may be altogether absent. 

 Young shells are often symphynote at the upper posterior angle. Beaks slightly 

 swollen and moderately convex, somewhat elevated above the hinge-line; placed 

 more or less anterior to the middle of the shell. Beak-sculpture (Marshall, 1890, 

 figs. 15, 18, as of A. lewisi) normally distinct and rather heavy, consisting of four 

 to five (rarely six) bars, of which the first an4 second are concentric, while the 

 following are distinctly double-looped, with a sharp re-entering sinus between the 

 loops. The anterior loop is broadly rounded, while the posterior is angular, 

 narrower, and characteristically elevated, so as to form a distinct tubercle. How- 

 ever, there is great variability in the beak-sculpture, chiefly with regard to the 

 development of the sinus and the tubercle. The former may be shorter or longer, 

 often so long as to reach the preceding bar; often the bar is weak at the sinus, so 

 that a notch is formed, the anterior and posterior loop being higher than this jDart. 

 The tubercles may be more or less distinct, and sometimes also the posterior end 

 of the anterior loop (close to the sinus) is tubercular, so that a double row of tub- 

 ercles appears to be present, radiating from the beaks. In partly eroded beaks, 

 often only the tubercles are preserved. 



Shell gently swollen in the middle and toward the beaks, but swelling very 

 variable, sometimes rather flattened on the disk. Posterior ridge indistinct, 

 greatest diameter of the shell about the middle. Posterior slope slightly com- 

 pressed, often elevated and winged at the upper posterior angle. 



Epidermis yellowish, greenish, to brownish and blackish. Rays indistinct as 

 a rule; in large specimens (and often also in younger ones), there is no trace of 

 rays on the disk. In other cases there are traces of green rays, but they are never 

 very distinct, and, when present, generally obliterated by the concentric color- 



"" Simpson (1900, p. 644) gives, with ??, southeastern Pennsylvania, but this is surely incorrect. 



