112 INVERTEBRATA OF MASSACHUSETTS. 



thick, inflated ; beaks placed at the anterior third, rather promi- 

 nent, usually very much eroded ; hinge margin straight, ascending 

 from before backwards ; anterior end narrow, regularly rounded ; 

 posterior end regularly curved above and below, and in the male 

 terminating in a distinct angle, but in the female very broadly 

 rounded ; a sharp ridge usually passes from the beaks towards the 

 posterior tip. Surface considerably undulated by the lines of 

 growth ; epidermis smooth, shining, and sometimes with rays of 

 minute wrinkles ; color dull greenish-yellow or light olive, usually 

 with rays of bright, dark-green, especially along the upper poste- 

 rior margin. Interior bluish-white, with sometimes a flesh-colored 

 tint. Cardinal teeth compressed and oblique ; lateral tooth rather 

 short; cavity of the beaks rather large. Length 3 inches, height 

 of male 1| inch, of female 2i inches, breadth Ij inch. 



Found in the Connecticut river and its tributaries, and in ponds 

 in Plymouth County. 



It is very difficult to fix upon characters which shall indicate this 

 shell, its variation in shape is so great. When young, it is thin and 

 beautifully radiated, and not easily distinguished from the young of 

 U. ochrdceus ; and at maturity, no species presents a greater contrast 

 between the male and female than this. As found in this region it is 

 quite thin, and radiated only along the posterior margin ; but in the 

 waters south of New England, it becomes larger and more solid. 



Unio ochraceus. 



Shell oblong, sub-ovate, inflated, thin, inequilateral angulai' 

 behind ; epidermis loosely wrinkled posteriorly, yelloicish-greenj 

 finely radiated with olive ; cardinal teeth compressed, nearly 

 parallel with the margin ; within salmon or rose-colored. 



Figure 74. 



State Coll., No. 174. Soc. Cab., 2203. 



Unio ochraceus, Say; JVich. Encijc. (^Amer. ed.) iv. pi. 2, f. 8. Lea ; Trans. Amer. 



Phil. Soc, (New Series,) vi. 126. pi. 15, f. 44. (animal). Synops. JVaiad., 23. 



Conrad; UnionidcB, 37, pi. 17, f. 2. 

 Symphynota ochracea, Lea ; Trans Jimcr. Phil. Soc, (New Series,) iii. 69. 



