NAYADES. 103 



a variety, Rossmassler, IV, p. 24, pi. 20, f. 283; Ziegler Mus.; 

 Anodonta rhomboidea, Schliit; Anodon complanata, Brown, 

 Illust. Conch., p. 80, pi. 28,* f. 6, 7. 



Shell very thin, compressed, elliptically-ovate ; the superior, 

 or hinge margin ascending, in a somewhat curved line, to the 

 termination of the ligament, from whence it descends and 

 terminates in a produced beak, quite at the lower angle 

 of the posterior side ; basal line very straight, with a slight 

 curvature; anterior margin rounded, and narrow, near to 

 which the slightly developed umbo is situate ; whole surface 

 with concentric wrinkles, and covered with a reddish-brown 

 epidermis. 



This variety is found in the river Calder, near Wakefield; 

 and it has been forwarded to me from the Trent, at Repton, 

 near Burton, by the kindness of Sir Oswald Mosley, Bart., a 

 gentleman distinguished for the deep interest which he takes in 

 the advancement of Natural Science. 



Variety 7. Avonensis, pi. XVIII, f. 3. 



Mi/tilus Avonensis, Montagu, Test. Brit., p. 172; Turton, 

 Brit. Fau., p. 165; Mytilus Cygneus, var. 13, Maton and Rack- 

 ett, Linn. Tr., VIII, p. 110, pi. 3 A, f. 3; Fleming, Edin. Ency., 

 VII, p. 99, pi. 206, f. 5 ; Anodonta Anatina, var., Rossmassler, 

 VI, p. 57, pi. 30, f. 418; Anodon Avo7iensis, Brown, Illust. 

 Conch., p. 80, pi. 29, f- 2. 



Shell ovoid, or subrhomboidal, ventricose, rather thick, in 

 some specimens very thick ; anterior margin rounded, short ; 

 posterior margin long, and pointed ; hinge line subarcuated ; 

 basal line slightly curved; external surface generally rough, with 

 sharp concentric wrinkles, covered with a very thick, variously 

 coloured, rather dull epidermis ; sometimes olivaceous, and at 

 others reddish-brown. 



This variety is subject to considerable variation of form and 

 size, and is in general well marked. It is usually of a dull 

 white internally, with but little of the pearly lustre so prevalent 

 in its congeners. 



Found in the Avon and New River; also near Tisbury, Wilt- 

 shire ; the Trent, near Burton ; near Steeton ; the canal, near 

 Halifax, and of a large size in the canal, near Sowerby Bridge, 

 Yorkshire. 



