680 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



Canthyria Swainsox, Tr. on Mai., 1840, p. 278. 

 Uniomerm Conkad, Pr. Ac. N. Sci. Pliila., VI, l!-53, p. 268. 



Shell iuequilateral, oval to elongated, rouuded iu frout aud poiuted 

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

 often becoming" slightly arcuate when oldj 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 fine 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 pseudocardinal 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 inner brauchite free from 

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

 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; papilhe on branchial and anal 

 openings unbranched; superaual opening always closed below. 



Section lYMNIUM Oken, 1815. 

 (Type, Unio pictorum Retzius.) 



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

 rugated or pustulous; i^seudocardinals compressed; beak cavities well 

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

 late or smooth. 



(Grioup of Unio piGtorum.) 



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; poste, 

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

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

 l>ressed, 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 Linnseus.! 



* Mya pictorum Linn^us, Syst. Naturai, 10th ed., 1758, I, p. 671; Fauu. Suec, 

 1761, No. 2129.— *MuLLER, Vermes, 1774, p. 211.— Pennant, Brit. Zool., IV, 

 1777? pi. XLiii, fig. 17.— "Da Costa, Hist. Nat. Brit., 1778, p. 228, pi. xv, 

 fig. 4. — ""SCHKOTEK, Flusscouch., 1779, p. 178, pi. in, figs. 2, 4, 5. — ''Born, 

 Test. Mas. VincL, 1780, p. 20.— * Schrotek, Eiu. Conch., 1783, II, p. 604.— 

 *Olivi, Zool. Adriatic, 1792, p. 95.— Sturm, Deuts. Faun., VI, 1803, 2d ed, 

 p. 19, pis. a, h, c. — -Montagu, Test. Brit., 1803, p. 36. — "Turton, Brit. Fauna, 



'Hauley says [Ipse Linntei Conchylia, p. 27] : "More Uniones than one are pres- 

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

 [Rossm. Icon., fig. 196] agrees best with synonymy and description. The figure 

 rei'erred to of Lister is U. pictorum ; Bonanui's drawing is more doubtful and was 

 possibly meant for U. Umiidus. The descriptions iu Fauna Suecica and Systema are 

 brief aud unsatisfactory and might suit either species alike." 



