170 



UNIONIDiE. 



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

 liecomes qnite dnsky, with darker and lighter zones alternating, and 

 delicate, rather oljscnre rays oi' dnsky. Within silvery-white, iri- 

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

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



Fio;. 473. 



U. nasutus. 



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

 Cavity of the l)eaks small. Length, three inches ; height, one and 

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



This species is rather rare. 1 have fomid it in Fresh Pond, Cam- 

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

 J. Whittemore found several good specimens in the ]\Iiddlcsex 

 Canal, not far iVoui 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 cons])icuons by a contraction of the basal mar- 

 gin just before the ti|i, and its compressed and ol)lique 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-ibbosus, 

 as the general form is the same, and the jjrolongation 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 teeth strong, erect, pyramidal. 



Mija radlata, Gmei.in, Syst. 3220. — Dillwyn, Catal. i. .51. — Wood, Gen. Conch. 109. 

 Unio radiata, Labiaiuk, An. sans Vert. vi. .'J35. — Deshayes, Encyc. Meth. Vers ii. 581. 



