176 BULLETIN OF THE NEW YORK STATE MUSEUM 



Unio Tappanianus, Lea 



Fig. 2 



Beaks with four or five undulations, each having a promi- 

 nent sinus on the ventral side about the middle, and plainly 

 visible converging lines both anteriorly and posteriorly. 

 Dorsal areas with several fine, direct, uninterrupted radiating 

 lines. 



The beaks of this species very closely resemble those of 

 Unio presstis, Lea, but the undulations are proportionally 

 stronger and are placed nearer the tip of the beak, and the 

 sinus is more nearly medial and not so deep. The radiating 

 lines on the anterior dorsal area are straight, sharply defined 

 against the surface of the shell and come to an abrupt 

 termination. Those of U. pressus are not so sharply de- 

 fined, are curved and wavering and gradually become 

 obsolete. 



Dr. Lea, in his Synopsis of the Unionidae, has the two 

 species widely separated, the one, U. Tappanianus, arranged 

 under non-symphynote, smooth, obovate Unios, and the 

 other, U. pressus, under symphynote, smooth, oblong Unios. 

 So far as this classification relates to U. Tappanianus, it is 

 erroneous. I have specimens of U. Tappanianus which are 

 symphynote for one-half or two-thirds the length of the 

 hinge-line. The possession of this character alone would be 

 sufficient to place Tappaniamis near to pressus in a system- 

 atic arrangement. Judged by the characters of the beaks 

 alone these two species appear to be closely related, and 

 there is no great difference in form or outline or other char- 

 acters of the shells to gainsay this evidence of the beaks. 

 U. Tappanianus is, perhaps as a rule, a more obese shell 

 than U. pressus, but the latter is sometimes quite as obese 

 as the former. 



Many growing and adult specimens of U. Tappanianus 

 show a linear depression of the surface of the shell from the 

 sinus in the undulations of the beaks to the middle of the 

 ventral margin. In all the specimens examined the depres- 



