NAIADES. MOLLUSC A. UNIO. 107 



GENUS NIO, BRUG. 



Shell equivalve, inequilateral; hinge with a stout, irregular, 

 striated, simple or divided cardinal tooth, in each valve, and an 

 elongated, compressed, lateral tooth extending along the margin. 



UNIO COMPLANA'TUS. 



Shell transversely ovate, somewhat angular posteriorly, inequi- 

 lateral ; beaks not much elevated , epidermis dark-brown ; interior 

 purple or salmon-colored ; hinge teeth deeply striated, pyramidal. 



FIGURES 68, 69, 70. 

 State Coll., No. 176. Soc. Cab., No. 2150. 



Mya complanata, SOLANDER; Mss., Portland CataL, 100. DILLWYN ; CataL, I. 



51. 



IPnio purpureus, SAY ; Nich. Encyc. (Amer. ed.,} iv. 3, f. 1. ( DESHAYES ; Encyc. 



M&tk., Vers, ii. 581, pi. 249, f. 5. BARNES ; Sillimaris Journ., vi. 216. 

 ITnio purpurascens, LAM., An. sans Vert., vi. 535. 

 U y nio violaceus, SPENGLER. 

 U^nio rarisulckta, coarctata, rhombula, carinifera, Georgina, glabrkta and sulci- 



dens of LAM. ; (An. sans. Vert., vi.) on the authority of Lea. 

 U^nio fluviatilis, GREEN. '*:<*.'. 



U^nio complanatus, LEA; Naiades, 30. Trans. Amer. Phil. Soc., (New Series,) 



Hi. 416, vi. 130, not of DESHAYES. 



Shell very variable in form, usually oblong-ovate, sometimes 

 sub-rhomboidal or sub-oval, very inequilateral, broadest behind, 

 rather compressed. Beaks about the anterior fourth of the shell, 

 little elevated, always much eroded, and exhibiting numerous 

 layers of greenish epidermal matter; anterior extremity always 

 regularly rounded ; superior margin, behind the beaks, straight and 

 somewhat ascending for one half its length, then, suddenly declin- 

 ing, it forms an indefinite angle ; posterior end pointed, rounded or 

 slightly clipped ; inferior margin regularly curved, or sometimes a 

 little arched at the middle ; an obtuse ridge passes from the beaks 

 to the posterior tip. Surface coarsely wrinkled by the lines of 

 growth, and covered by a dark, tar-colored, or very dark-green 

 epidermis. Interior usually of a beautiful dark peach-blpsom 

 color, and passes from this through salmon-color to mother-of- 



