1 86 BULLETIN OF THE NEW YORK STATE MUSEUM 



thickened on the anterior margin and more delicately finished 

 in all particulars than those from the other localities in 

 the state. The beaks in Norman's Kill specimens are more 

 nearly in the middle of the hinge-line than in specimens 

 from other localities. 



Anodonta undulata, Say 



Fig. 12 



Beaks with four prominent undulations, which are placed 

 very obliquely with reference to the hinge-line, and which 

 are rounded anteriorly and angular posteriorly. Posteriorly, 

 the undulations have very prominent, straight, continuous 

 converging lines. Anteriorly, the converging lines, though 

 distinct, are much less prominent. Dorsal areas with sev- 

 eral straight radiating lines which are more prominent 

 posteriorly than anteriorly. 



The undulations of the beaks of this species very closely 

 resemble those of An. edentula, but careful comparison of 

 the two species will t reveal several slight differences. The 

 fine radiating lines on the posterior dorsal area are more 

 prominent and more numerous in An. edentula than in An. 

 undulata, and the former has more distinct radiating lines 

 on the anterior dorsal area. The most important difference 

 between the two species is in the relative positions of the 

 undulations. In An. edentula the stoutest portion of each 

 undulation is nearly parallel to the hinge-line, while in An. 

 undulata the stoutest portion of each undulation is decid- 

 edly oblique with reference to the hinge-line. 



The differences between the beaks of An. undulata and 

 An. Ferrusaciana are slight. The latter is intermediate 

 between An. undulata and An. edentula. The undulations 

 of Ferrusaciana are not so strong as those of the two 

 species just mentioned ; the posterior converging lines are 

 extremely fine ; and the anterior converging lines are obso- 

 lete. The posterior dorsal area has many radiating lines 

 much finer and more numerous than in An. undulata; the 

 anterior area shows no trace of radiating lines. 



