680 VlUH-KKDiydS OF Till: XATIO.\.U, M I'SEUM. 



Canthyria SWAINSON, 'I'r. on Mai., 1810, p. 27X. 



H* CONRAD, Pr. Ac. N. Sci. Phila., VI, lN r >S, p. 268. 



Shell inequilateral, oval to elongated, rounded in front and pointed 

 or biaugulate behind, with a more or less developed posterior ridge, 

 often becoming slightly arcuate when old; beaks only moderately full, 

 generally sculptured with coarse ridges, which run parallel with the 

 growth lines, or are somewhat doubly looped, sometimes broken and 

 showing flue radiating lines behind ; surface smooth, slightly concentric- 

 ally ridged or pustulous ; epidermis generally rather dull colored, rayless 

 or feebly rayed; hinge plate narrow; two pseudocardinals and two lat- 

 erals in the left valve and one pseudocardiual and one lateral iu the 

 right, with rarely a vestige of a second lateral; cavity of the beaks 

 not deep or compressed. Animal having the iniier branchiae free from 

 the abdominal sac for from one-half to their entire length; marsnpiuin 

 occupying the whole length of the outer gills only, forming a thick, 

 smooth pad when filled with young; gills united to the mantle behind 

 to their extreme points, or very nearly so ; papilla; on branchial and anal 

 openings unbrauched; superanal opening always closed below. 



Section IYMNIUM Oken, 1815. 

 (Type, Unio pictorum Retzius.) 



Shell generally smooth; beak sculpture broken, often somewhat cor- 

 rugated or pustulous; pseudocardinals compressed; beak cavities well 

 excavated, not compressed. Animal highly colored, anal opening crenu- 

 late or smooth. 



(Group of Unio pictorum.} 



Shell inflated, elongate, oval, anterior end angled above, swollen a 

 little at posterior base; beaks full, their sculpture consisting of numer- 

 ous slightly doubly looped bars which often become pustulous; paste, 

 rior ridge rather low; epidermis smooth, rather bright, sometimes 

 slightly rayed behind; rest periods well marked ; pseudocardinals com- 

 pressed, often a little reflexed, smooth below, those of the left valve 

 partly united; muscle scars smooth; nacre whitish to salmon. Animal 

 the same as described for the section. 



tUNIO PICTORUM Linnaeus. 1 



* Mya pictorum LINN/EUS, Syst. Naturaj, 10th ed., 1758, I, p. 671; Faim. Suec., 

 1761, No. 2129. *MiiLLER, Venues, 1774, p. 211. PENNANT, Brit. Zool., IV, 

 1777? pi. XLIII, fig. 17. *DA COSTA, Hist. Nat. Brit., 1778, p. 228, pi. xv, 

 fig. 4. ^SCHHOTER, Flusscouch., 1779, p. 178, pi. in, figs. 2, 4, 5.* BORN, 

 Test. Mus. Vind., 1780, p. 20. *SCHROTEK, Ein. Conch., 1783, II, p. 604, 

 *OLivi, Zool. Adriatic, 1792, p. 95. STURM, Deuts. Faun., VI, 1803, 2d ed, 

 p. 19, pis. a, b, c.* MONTAGU, Test. Brit., 1803, p. 36. ; TURTON, Brit. Fauna, 



'Hanley says [Ipse Linntui Couchylia, p. 27] : "More Uniones than one are pres- 

 ent in the [Linuaum] collection, but upon the whole the U. pictorum of authors 

 [Rossui. Icon., tig. 196] agrees best with synonymy and description. The figure 

 referred to of Libter is U. pictorum; Bonanni's drawing is more doubtful and was 

 possibly meant for I', tiimidiis. The descriptions in Fauna Suecica and Systema are 

 brief and unsatisfactory and might suit either species alike." 



