uNio. 167 



the hinge or the form of the shell ; and more recently Professor 

 Agassiz has proposed several genera, not yet published, founded on 

 the peculiarities of the animal, especially of the mantle and the 

 parts of the gills which carry the embryos. 



OciiHS UNIO, Retzius. 1788. 



Shell equi valve, inequipartite, multiform ; hinge with a stout, 

 irregular, striated, simple or divided cardinal tooth in each valve, 

 and an elongated, compressed, marginal tooth ; gills free from the 

 abdominal sac, their posterior extremity attached to the mantle ; 

 eggs filling the whole extent of the outer gill ; upper siphonal open- 

 ing somewhat fringed. 



Ig, OWX^^^YY^lO-U XX^XXgv 



Unio complanatus. 



Figs. 68, 69, 70. 



Shell elongated ovate, somewhat angular posteriorly, inequipartite ; beaks not 

 much elevated, epidermis dark brown ; interior purple or salmon-colored ; hinge- 

 teeth deeply striated, pyramidal. 



Mya complanata, Solander, MSS., Portland Catal. 100. — Dillwyn, Catal. i. .51. 

 Unio purpureus, Say, Nich. Encye. (Amer. 1st ed.) iv. 3, fig. 1 (1816). — Deshayes, 



Encyc. Me'th. Vers., ii. 581, pi. 249, fi<;-. 5. — Barnes, Silliman's .Jouni. vi. 264. 

 Unio purpurascens, Lamarck, An. sans Vert. 2d ed. vi. 53.5. 

 Unio violaceus, Spengler, in Guerin's Mag. 26. 

 Unio rarisulcata, coarctata, rhombula, carinifera, Georgina, glabmta, and stdcidens of Laji. 



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

 Uniofluviatilis, Green. 

 Unio complanatus, Lea, Naiades, i. 30; Trans. Amer. Phil. Soc. (new series) iii. 416 



(1830) ; vi. 130, not of De.shayes. — De Kay, Nat. Hist. N. Y. 188, pi. 22, fig. 246. 



Shell very variaiile in form, usually oblong-ovate, sometimes sub- 

 rhomboidal or sub-oval, very inequilateral, l)roadest 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 some- 

 what ascending for one half its length, then, suddenly declining, 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. 



