100 NAYADES. 



teristics of which we shall endeavour to point out. Most of 

 the Anodons undergo considerable change, in their progress 

 from the young to the adult condition. 



Variety 1. Cygneus, pi. XI, f. 1,2, 3. 



AnodontaCygnea, Pfeiffer, 1, p. ill, pi. 6, f. 4; Rossmassler, 

 I, p. 1 1 1, pi. 3, f. 67; lb., V, VI, pi. 25, f. 342; Mytilus Cyg- 

 neus, Pennant, Brit. Zool., IV, p. 113, pi. 67> f. 78; Donovan, 

 Brit. Sh., pi. 55 and 113; Maton and Rackett, Linn. Tr., VIII, 

 p. 109, pi. 3 A, f. 2 ; Sheppard, Linn. Trans., XIII, pi. 5, f. 3 ; 

 Montagu, Test. Brit., p. 170; Fleming, Edin. Ency., VII, p. 96, 

 pi. 205, f. 16; Thompson, Ann. and Mag. Nat. Hist., VI, p. 40; 

 Anodon Cygnea, Alder, Mag. Zool. and Bot., II, p. 117; Ano- 

 don Cygneus, Brown, Illust. Conch., p. 79j ph 28, f. 1, 3, 4. 



Shell rather thin, oblong-ovate, inflated ; umbo small, placed 

 near the anterior side, which is rounded and short ; posterior 

 side elongated, with the hinge line nearly parallel, or slightly 

 obhquc, from whence it suddenly slopes into a subrostrated 

 form; lower margin rounded, gradually sloping upwards towards 

 the posterior side ; external surface concentrically wrinkled, 

 and covered with an olive-green, shining epidermis ; inside 

 pearlaceous. 



Figs. 2 and 3, young shells. 



Found in the river Ouse, at York; the Thames, near "Wind- 

 sor; in the ponds at Elmingham Park, the seat of the Countess 

 of Dysart, Suffolk ; Loch Kettrine, Scotland ; in the Grand 

 Canal, and the Moyntaghs, County of Armagh, Ireland ; and 

 many other lakes and rivers in Britain and Ireland. 



Variety 2. Cellensis, pi. XII, f. 1, 2. 



Anodonta cellensis, Encyclopedia Methodique, pi. 202; Pfeif- 

 fer, I, p. 110, pi. 6, f. 1 ; Rossmassler, IV, p. 23, pi. 19, f. 280; 

 Anodon cellensis, Alder, Mag. Zool. and Bot., II, p. 118; Ano- 

 don Cygneus, Drapernaud, Moll., pi. 12, f . 1 ; Turton, Man., 

 pi. 1, f . 8 ; Anodon paludosus, Turton, Brit. Biv., p. 240, pi. 

 15, f. 6; Anodonta sulcata, Lamarck, An. San. Vert., V, p. 85; 

 Mytilus cellensis, Schroeter, Flussconch., pi. 2, f. 1 ; Mytilus 

 anatinus. Pennant, Brit. Zool., IV, p. 1 13, pi. 68, f. 79; Maton 

 and Rackett, Linn. Tr., VIII, p. 110, pi. 3 a, f . 1 ; Montagu, 

 Test. Brit., p. I7l ; Sheppard, Linn. Trans., XIII, pi. 5, f. 5 ; 

 Fleming, Edin. Ency., VII, p. 99, ph 204, f. 14 ; Anodon cel- 

 lensis, Brown, Illust. Conch., p. 79, pi- 28,* f. 1,2. 



