170 



UNIONIDiE. 



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

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

 delicate, rather obscure rays ol" dusky. Within silvery-white, iri- 

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

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



Fig. 473. 



U. nasutus. 



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 ponds in Plymouth. Mr. T. 

 J. Whittemore Ibund several good specimens in the jMiddlesex 

 Canal, not far IVom Charlestowu. 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 tij), and its comjiressed and oblique teeth, are 

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

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

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

 not then very remarkable. 



Unio radiatus. 



Fig. 73. 



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

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

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



Myn rwliatn, Gmelin, Syst. .3220. — Dillavyn, Catal. i. .51. — Wood, Gen. Concli. 109. 

 Unio rudiata, Lamakck, An. sans Vert. vi. r).S5. — Deshayes, Encyc. Moth. Vers ii. 581. 



