NAIADES. MOLLUSCA. UNIO. 109 



livid, the shell never becomes so large, is more regularly convex ; the 

 epidermis is nearly smooth, shining and yellowish-green, with conspicu- 

 ous rays of olive color. 



Unio nasutus. 



Shell transversely oblong-lanceolate, hinge margin compressed., 

 anteriorly rounded, posteriorly somewhat healied ; epidermis dusky- 

 green, obscurely rayed ; cardinal teeth compressed, oblique ; nacre 

 very bright, bluish-white, iridescent. 



Figure 71. 



State Coll., No. 178. Soc. Cab., No. 2158. 



Unio nasutus, Say; Mch. Encyc, {Am. ed.) iv. pi. 4, f. 1. Conrad ; Unionida. 

 Mya nasuta, Wood ; Index, Suppl., pi. 1, f. 4. 



Unio rostit\tus, Valenc. ; Recueil d' Obs. de Zool., (^"C, par Humb. ct BonpL, ii. 

 233. pi. 53, f. 3. Lister ; Conch., 1. 15] , f. C. 



Shell slender, oblong-lanceolate, very inequilateral ; beaks, 

 small, pointed, and slightly elevated ; hinge margin straight to 

 more than half the distance from the beaks to the posterior end, 

 when it suddenly declines and continues straight to the point ; 

 lower margin nearly parallel with the upper, though somewhat 

 rounded at the middle, and towards the end turns rapidly upward 

 towards the point, which is considerably produced, so as to form 

 a sort of snout. An angular ridge passes backwards from the 

 beaks to the tip, above which the shell is very much compressed ; 

 two or more radiating furrows are usually seen traversing this por- 

 tion. Surface rather smooth, not much wrinkled by the lines of 

 growth. Epidermis 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 of 

 dusky. Within, silvery white, iridescent, and oftentimes with 

 shades of bluish or salmon-color. Hinge with the cardinal teeth 

 rather delicate, compressed, and directed obliquely forwards, so 

 as to look to the middle of the front. Cavity of the beaks small. 

 Length 3 inches, height li inch, breadth 4 inch. 



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

 Cambridge, and have received it from the ponds in Plymouth. 



