CONCHACEA. 117 



margin ; an indistinct, pretty large, muscular impression near 

 the anterior margins, and a narrower, obscure one in the pos- 

 terior sides. 



This is the largest species of the genus, sometimes mea- 

 suring five-eighths of an inch in length, and seven-eighths in 

 breadth. 



Found plentifully in the Thames at Battersea, and also near 

 Red House, and in the neighbourhood of Oxford ; of a large 

 size in the Trent, near Burton ; and in many slow rivers in 

 England. 



2. Cyclas cornea, pi. XXIII, f. 4. 



Ci/clas cornea, PfeifFer, p. 120, pi. 5, f. 1, 2; Turton, Brit. 

 Biv.,'p. 248, pi. 11, f. 14; lb., Man., p. 13, f. 2; Fleming, Brit. 

 An., p. 452 ; Forbes, p. 49 ; Thompson, Ann. and Mag. Nat. 

 Hist., VI, p. 52; Alder, Mag. Zool. and Bot., II, p. 118; Brown, 

 Illust. Conch., p. 93, pi. 39, f. 19 ; lb., First Ed., pi. 17, f. 15 ; 

 Cyclas 7'ivalis, Drapernaud, Hist, des Moll., II, p. 202, No. 387; 

 Tellina co7'nea, Gmelin's Linne, I, p. 1120, No. 72. 



Shell subglobular, ventricose, thin, semitransparent ; with 

 concentric, nearly obsolete strife ; umbones obtuse ; epidermis 

 greenish horn-colour, with darker zones, and bordered with a 

 broad, yellowish band ; inside dull bluish-white. Length three 

 and a half eighths of an inch ; breadth half an inch. 



A very distinct variety, considerably less than the ordinary 

 size, with the teeth larger in proportion, and of a lemon-yellow 

 colour, was found by Mr. Glover, in the Leven, not far from 

 Ambleside. 



Found in most water streams, and in stagnant ditches and 

 pools, throughout Britain and Ireland ; is common in Dudding- 

 ston Loch, near Edinburgh, of the size above described, which 

 is considerably more than its ordinary dimensions. 



This shell is readily distinguished from the C. rivicola, by its 

 more ventricose shape, in being thinner, more transparent, and 

 seldom measuring above half the size of the former. 

 3. Cyclas lacustris, pi. XXIII, f. 5. 

 Cyclas lacustris, Drapernaud, Hist, des Moll., p. 130, pi. 10, 

 f. 6, 7 ; Lamarck, V, p. 559, No. 3 ; Turton, Man., p. 14, f. 4 ; 

 Pfeiffer, p. 122, pi. 5, f. 6, 7 ; Fleming, Brit. An., p. 453; 

 Thompson, Ann. and Mag. Nat. Hist., VI, p. 52; Brown, Illust. 

 Conch., p. 94, pi. 39, f. 20 ; lb,. First Ed., pi. 17, f. 16. 



