188 NEW-YORK FAUNA — MOLLUSCA. 



GENUS UNIO. Bruguieres. 



Animal with its mantle open throughout beneath, with thick edges, often fringed. A short 

 posterior incomplete tube, furnished with two series of tentacular papillae, subserving the 

 purposes of respiration : triangular labial appendices. Gills moderately long, unequal, on 

 the same side. Foot large, thick, rounded or subquadrangular. Shell : hinge with a stout, 

 irregular, striated, simple or divided cardinal tooth in each valve, and an elongated com- 

 pressed lateral tooth extending along the margin. 



Obs. The shells of this and the other genera are popularly known under the names of 

 Freshwater clams and mussels. 



Unio complanatus. 



plate xxii. fig. 246.; 



(STATE COLLECTION.) 



Mya complanata, Solander. Dillwyn, Cat. Vol. 1, p. 51. 



Unio purpureas. Sxy, Nich. Ency. pi. 3, fig. 1. 



V. id. Barnes, Am. Jour. Sc. Vol. 6, p. 264. 



Margarita (Unio) complanata. Lea, Synopsis, Am. Phil. Tr. Vol. 6, p. 130. 



U. complanatus. Russel, Essex Am. Jour. Vol. 1, p. 59. Adams, Am. Jour. Vol. 40, p. 276. 



U. id. GouiD, Invertebrata of Mass. p. 117, figs. 68, 69, 70. 



Description. Shell varying from fragile to robust, oblong, very inequilateral. Ligament 

 thick and stout, transversely ovate or more usually subrhomboidal, broadest behind, where 

 the margin descends nearly in a straight line from the hinge-margin to the posterior extremity, 

 which is subacutely rounded : lower margin regularly curved, occasionally slightly arched in 

 the middle ; hinge-margin elevated, compressed and carinate. Beaks usually much decorti- 

 cated ; anterior extremity regularly rounded. Hinge-teeth in one valve erect and strongly 

 striated ; in the other, bifid : lateral teeth elongated, slightly curved. 



Color. Epidermis dark olive-green, occasionally in the young with faint narrow radiations : 

 within bluish or silvery white, purple, reddish, greenish, sometimes one uniform color, and 

 occasionally all intermixed. 



Length, 1*5- 2' 5. Transverse diameter, 2*5- 4*5. 



This is a common species in almost every part of the State. I am indebted to Dr. Eights 

 for the observation that this, as well as other fluviatile bivalves, are more perfect and ponder- 

 ous in the canals and ponds than in quick running streams. Specimens obtained from Little- 

 falls and Oak-orchard, were of a uniform dull reddish or purplish hue within. 



