162 MEMOIRS OF THE CARNEGIE MUSEUM. 



and Potomac drainages. Altogether it seems to me, that this form is more northern 

 in its distribution, and the majority of localities are from New York, Connecticut, 

 and Massachusetts, in which direction it goes as far as Maine (Lermond, 1909). 

 Generally it is reported as living in ponds, but sometimes also in rivers. The 

 locahty in the deep channel of the Delaware (35 to 45 feet depth), given above, is 

 quite interesting and possibly suggestive. Further studies on this species are very 

 desirable. (See Ortmann, 1913a, p. 363.) 



Anodonta ohiensis Rafinesque (1820). 

 Anodonta iuibecillis Say. Simpson, 1914, p. 395; Lastena ohiensis (Rafinesque) 

 Utterback, 1916, p. 109.''^ 



Plate XI, fig. 4. 

 Records from Pennsylvania: 



Ortmann, 19096, p. 195 and 202. 



Characters of the shell: Shell small, at the utmost of medium size, very thin. 

 Outline subelliptical, rather elongate, rounded anteriorly, narrowed and somewhat 

 pointed behind. Ldwer margin gently convex, less so in the posterior part, some- 

 times almost straight in the middle. Upper margin straight, forming a more or 

 less distinct angle with the obliquely descending posterior margin, and in general 

 this angle is elevated to form a wing, which is rarely entirely obliterated. Beaks 

 depressed, and not at all elevated above the hinge-line. In young shells the beaks 

 slope down obliquely (roof-like) from the hinge-line; in older, more swollen shells, 

 they are nearly or entirely horizontal. Beaks placed anterior to the middle of 

 the shell. Beak-sculpture fine, weak, and irregular, consisting of four to six 

 subconcentric ridges, of which the later ones have a faint sinuation, which is only 

 wavy, and does not form an angle. Often this sinus is represented only by an 

 interruption of the bar. 



Shell of young specimens very slightly swollen, or even compressed; in older 

 ones it becomes more inflated, and assumes in extreme cases an almost subcylindrical 

 shape. Posterior ridge very indistinct, rounded; greatest diameter of the shell 

 about in the middle. Posterior slope more or less compressed and elevated into 

 the wing of the upper posterior angle. 



Epidermis lighter or darker green, often beautifully grass-green, grajash, 

 brownish, or yellowish near the beaks, with concentric, darker growth-rests, and 



"' I object to the use of the generic name Lastena for this species. It is not the type of Rafinesque's 

 subgenus Laslcna, and a type for this genus was not designated until Simpson (1900, p. 654), selected 

 lata Rafinesque for it. It might possibly be desirable to generically separate this species from the other 

 species treated in Ihis paper under Anodonta, but in this case, a new name should be found. 



