NAYADES. 105 



whence it suddenly declines towards the somewhat truncated 

 extremity ; basal line considerably arcuated ; exterior surface 

 but slightly wrinkled transversely ; umbones small, and acute ; 

 inside bluish-white, with faint pearlaceous reflections. 



This variety differs from the A. piscinalis, in being more 

 ponderous, and more inflated, in the hinge line being more 

 arcuated, and in being less rostrated. 



Found in the Irwell, near Manchester, by my esteemed 

 friend Mr. Samuel Gibson, of Hebden Bridge, Yorkshire, to 

 whom I am indebted for specimens ; and also in a lodge at 

 Dinting Vale, near Glossop, by my friend Mr. Robert Darby- 

 shire, of Manchester. 



Variety 10. Piscinalis, pi. XVII, f. 3, 4, 5. 



Anodonta piscinalis, Nilsson, p. 116, No. 3; Drapernaud, 

 Hist, des Moll., pi. 12, f. 2; Rossmassler, IV, p. 23, pi. 19, f. 

 281 ; Anodonta ventricosa, Pfeiffer, II, p. 30, pi. 3, f. 6; Alder, 

 Mag. Zool. and Bot., II, p. 118; wood cut, Kenyon, Mag. Nat. 

 Hist., I, f. 188; Mytilus macidatus, Sheppard, Linn. Trans., 

 XIII, pi. 5, f. 6, young shell; Anodon piscinalis, Brown, Illust. 

 Conch., p. 80, pi. 28,* f. 3, 4, 5. 



Shell subovate, ventricose, thick ; hinge hne ascending in a 

 waved, subarcuated sweep towards the posterior side, and des- 

 cending in a hollow bent line, ending in a produced, turned 

 upwards beak ; basal margin considerably arcuated, and ascend- 

 ing rather abruptly towards the posterior side ; outer surface 

 covered with a thick, shining, olivaceous epidermis, with many 

 obscure, radiating lines of a darker hue. 



Found in the canal, near Birmingham ; and in Combermere, 

 Cheshire, where I procured an extensive series, while on a visit 

 at the Abbey, through the polite attention of Viscount and 

 Lady Combermere. 



Varietij 11. Rostrata, pi. XVI, f. 1, 2. 



Anodonta rost^'ata, Kokeil Museum; Rossmassler, IV, p. 25, 

 pi. 20, f. 284 ; Brown, Illust. Conch., p. 80, pi. 28,* f. 8, 9. 



Shell compressed, considerably elongated transversely, thin ; 

 anterior side very short; posterior side very long, and produced 

 into a somewhat lengthened, blunted beak; hinge line arcuated, 

 and ascending, its greatest altitude being nearly central ; ante- 

 rior side rather narrow, and rounded; posterior side descending 

 in a waved line ; basal line nearly parallel, and undulating ; 



P 



