170 



UNIOXID^. 



somewhat glossy, of a dark olive-green color, which in old shells 

 becomes quite dusky, with darker and lighter zones alternating, and 

 delicate, rather oljscure rays of dusky. Within silvery-wdiite, iri- 

 descent, and oftentimes with shades of bluish or salmon-color. 

 Hinge with the cardinal teeth rather delicate, compressed, and di- 



Fisr. 473. 



rected obliquely forwards, so as to look to the middle of the front. 

 Cavity of the beaks small. Length, three inches ; height, one and 

 one fourth inches ; breadth, four fifths of an inch. 



This species is rather rare. I have found it in Fresh Pond, Cam- 

 bridge, and have received it from the jionds in Plymouth. Mr. T. 

 J. Whittcmore found several good specimens in the Middlesex 

 Canal, not far from Charlestown. It is more common in the Mid- 

 dle States. 



It is not difficult to distinguish this from any of the species found 

 in Massachusetts. The prolongation of the posterior extremity, 

 which is made more conspicuous by a contraction of the basal mar- 

 gin just before the tip, and its compressed and oblique teeth, are 

 well-marked characteristics. But it is not so easy to distinguish 

 smaller specimens of this from those of Z7. rectus and U. g-ibbosus, 

 as the general form is the same, and the prolongation of the tip is 

 not then very remarkable. 



Unio radiatus. 



Fig. 73. 



Shell transversely olDlong-ovate, broadest and angular behind, inequilateral; 

 epidermis wrinkled, brownish-olive, zoned and rayed with dusky-green; within 

 bluish-white ; cardinal teeth strong, erect, pyramidal. 



Mf/a radlatn, Gmelix, Syst. 3220. — Dillwyx, Catal. i. 51. — Wood. Gen. Conch. 109. 

 Unio radiata, Lamakck, An. sans Ycrt. vi. 533. — Deshayes, Encyc. Me'th. Vers ii. 581. 



