FAMILY LYMNjEACEA. 171 



1. Ancylus fluviatilis. River Ancylus. 



Shell ; somewhat rotundately ovate, more or less elevated, radiately 



wrinkled and striated, the striae being some- 

 times neatly defined, sometimes obscure, 



bluish white, covered with an olivaceous 



epidermis ; vertex sharply incurved to the 



right, quite behind. 

 A ncylus fluviatilis, Muller (1774), Term. Hist, part 



ii. p. 201. 



Patella fluoiatilis, Grmelin (1778), Syst. Nat. p. 3711. 

 Patella cornea, Poiret (1801), Coq. cle VAisne, p. 101. 

 Ancylus riparius, Desmarest (1814), Bull. Soc. Philom. p. 19. pi. i. f. 2. 

 Ancylus capuloides, Jan (1838), Porr. Mai. Terr, e Fluv. p. 87. pi. i. f. 7. 

 Ancylus, vitra< eus, strictus, and obtusus, Morelet (1845), Moll, du Port, p. 



87, 88. pi. viii. f. 3, 4, 5. 

 Ancylus deperditus, Dupuy (1851), Hist. Moll. vol. v. p. 494. pi. xxvi. f. 4. 

 Ancylus Janii, simplex, gibbosus, Deshayesianus, and cyclostoma, Bour- 



guignat (1853), Joum. Conch, p. 183 to 187. 

 Ancylus (Ancylasirum) fluviatilis , Moquin-Tanclon (1855), Hist. Moll. vol. 



ii. p. 484. pi. xxxv. f. 5 to 38, and pi. xxxvi. f. 1 to 49. 

 Hab. Throughout Europe. Algeria. Madeira. (Adhering to stones, and, 



less frequently, to plants, in shallow streams and running brooks.) 



In this species the respiratory and more important organs of the 

 animal are situated on the left side, and the subspiral vertex of the 

 shell, — showing that the mollusk commenced life with a tendency to 

 follow the spiral plan of growth, — is turned to the right. The body 

 is of a finely speckled slate- colour, and the head, as represented in 

 our vignette, is broad with the tentacles slenderly triangular and 

 widely separated, the eyes being small and distinct at their inner 

 base. The shell of A. fluviatilis , though thin, is of a firm sym- 

 metrical growth, rayed with fine ridges and striae, orbicularly ovate 

 at the base, and rising, cap-like, into a broad cone, is sharply 

 hooked at the posterior summit, with its embryonic nucleus turned 

 subspirally to the right. It chiefly inhabits gently running streams. 



The geographical range of this species appears to be very gene- 

 ral throughout Europe, and it extends to North Africa and Ma- 

 deira. More than a dozen species have been made of its different 

 varieties. Mr. Cuming possesses a well-authenticated series of 

 these alleged species, but they will scarcely bear the test of com- 

 parison when viewed with a due consideration of the conditions 



