ANCYLIDiE. 95 



Mag. Nat. Hist., VI, p. 47; Lamarck, VI, pt. 2nd, p. 27; 

 Patella Jiuviatilis, Montagu, p. 484; Linne, p. 1253; Da Costa, 

 p. 48, pi. 3, f. 8 ; Patella lacustris, Donovan, pi. 147, f. 2 ; 

 Maton and Rackett, p. 232 ; Brown, Ency. Brit., VI, p. 466 ; 

 lb., Wernerian Mem., II, p. 533; Crepedula lacustris, Fleming, 

 Edin. Ency. ; Ancylus Jiuviatilis, Brown, Illust. Conch., p. 59, 

 pi. 12, f. 1, 4, and 6 ; lb., First Ed., pi. 36, f. 1, 4, and 6. 



Shell subconic, with the vertex sharp, slightly recurved, and 

 situate near one end, sometimes a little hooked; pellucid, horn- 

 coloured, covered with a dark greenish-brown epidermis, some- 

 times of a paler hue, beneath which the shell is of a brown 

 horn-colour, and with a few concentric wrinkles; aperture oval; 

 marginal lip thin ; inside glossy, of a bluish-white. Length 

 three-eighths of an inch ; breadth a quarter of an inch. 



A variety is sometimes found, particularly in a stream near 

 Folkstone, in Kent, finely striated longitudinally. Montagu 

 says this variety is so strongly striated, that it was by some 

 considered a distinct species. He adds, " these were of an 

 inferior size, and covered with a dusky epidermis, differing in 

 nothing but the striae being more conspicuous." 



Common in most rivers and streams in Great Britain and 

 Ireland, adhering to stones at the bottom. 



Section II. — Animals dextral. 



2. Ancylus lacustris, pi. X, f. 4, 5, 6. 



Anci/lus lacustris, Miiller, Verm., II, p. 199; Drapernaud, 

 p. 47, pi. 2, f. 25, 26, 27; Pfeiffer, p. 109, pi. 4, f. 46; Lamarck, 

 VI, pt. 2nd, p. 27 ; Fleming, Brit. An., p. 280 ; Alder, Mag. 

 Zool.and Bot., II, p. 116; Turton, Man., p. 141, pi. 10, f. 126; 

 Thompson, Ann. and Mag. Nat. Hist., VI, p. 47 ; Patella 

 lacustris, Linne, Syst. Nat., p. 1260, No. 769; Pennant, Brit. 

 Zool., IV, p. 142; Montagu, Test. Brit., p. 484; Donovan, 

 Brit. Sh., pi. 150; Brown, Wernerian Mem., II, p. 533; lb., 

 Ency. Brit., VI, p. 466 ; Patella ohlonga, Maton and Rackett, 

 Linn. Tr., VIII, p. 233 ; Lightfoot, Phil. Trans., LXXVI, p. 

 168, pi. 3, f. 1 ; Anci/lus lacustris, Brown, Illust. Conch., p. 60, 

 pi. 12, f. 3, 5, and 7 ; lb.. First Ed., pi. 36, f. 3, 5, and 7- 



Shell conical, and of a much elongated, oval form, com- 

 pressed on the sides, thin, smooth, but not glossy, or slightly 

 wrinkled, nearly membranaceous, subpellucid. of a pale horn- 



