62 LAND AND FRESH-WATER SHELLS. 



3. Unio. Shell firm, solid, cardinal teeth large, lateral teeth 

 lamelliform. 



(a) Shell oblong, ovate, solid, brown ; epidermis smooth ; 

 umbones prominent, rugose, excentric ; anterior teeth high, conical, 

 strong. Length 3 inches ; width | inch. Canals, ponds, rivers. 



U. tumidus. 1 



(b) Shell oblong, ventricose, wedge-shaped, greenish-yellow 

 marked with brown in lines of growth ; ligament parallel to lower 

 margin, longer than in U. tumidus ; umbones not so prominent 

 nor so rugose as in U. tumidus; anterior teeth arched, much 

 compressed ; hinder teeth of left valve small or evanescent. 

 Length 2 to 3 inches. Ponds, lakes, and slow running streams. 



U. Pictorum? 



(c) Shell black-brown, elongated, ovate, thick, heavy, strongly 

 striated, very compressed ; umbones incurved, generally eroded, 

 excentric ; cardinal teeth small, slightly compressed, thick, sub- 

 triangular, conical, the posterior one of the left valve much 

 developed. Length 5! inches; width 2| inches; breadth i inch. 

 Among the gravel and small stones in the shallows of quick 

 running rivers or mountain torrents; U. margaritifer? 



4. Anodonta. Shell thin, hinge without teeth. 



(a) Shell very large, oval, thin, dull green, more or less dusky ; 

 lines of growth large ; umbones small, plaited ; ligament long, 

 parallel to lower margin ; posterior side gaping and produced into 

 a rounded cuneiform point. Length 2| to 4 inches; breadth 

 3 to 9 inches. Lakes, ponds, canals, and muddy rivers. 



A. cygnea 



(b) Shell smaller than A. cygnea, oval, compressed behind, 



7 v. radiata, thinner, greenish with yellow rays, hinge-line nearly straight ; 

 v. ovalis, wedge-shaped, dark olive-brown. 



8 v. radiata, yellowish with green rays ; v. latior, broader, shorter, 

 yellowish-brown ; v. curvirostris ', smaller, shorter, bent, olive-coloured ; v. 

 rostrata, slightly more elongated, lanceolate behind, brownish. 



9 v. Roissyi, less arched above, not sinuous below, larger posteriorily ; v. 

 sinuata, broader in proportion to length than type, yellowish- brown, lower 

 margin incurved towards the middle. 



10 v. ventricosa, shell larger, more elongated, more ventricose ; v. radiata, 

 larger with yellow rays ; v. Zellensis, yellowish-brown, broader, upper and 

 lower borders nearly parallel ; v. pallida, light yellow or fawn colour ; v. 



