200 BRITISH MOLLUSKS. 



2. Valvata cristata. Crested Valvata. 

 Shell ; minute, discoid, very largely superficially umbilicated, dull 



horny, whorls three and a half to 



four, rounded, narrow, increasing qd 



slowly, smooth or minutely striated, 



spire rather sunk, with the sutures 



impressed ; aperture small, round, 



with the lip thinly reflected. 

 Valvata cristata, Miiller (1774), Verm. Hist, part ii. p. 198. 

 Nerita valvata, Gnielin (1788), Syst. Nat. p. 3675. 

 Valvata pulchella, Studer (1789), Coxe, Trav. in Switz. toI. iii. p. 436. 

 Valvata planorbis, Draparnaud (1801), Tail. Moll. p. 42. 

 Helix cristata, Montagu (1803), Test. Brit. vol. ii. p. 460. vign. i. f. 7 and 8. 

 Valvata spirobis, Draparnaud (1805), Hist. Moll. p. 45. pi. i. f. 32 and 33. 

 Trochus cristatiis, Maton and Rackett (1807), Trans. Linn. Soc. vol. viii. 



p. 169. 

 Turbo cristatus, Turton (1819), Conch. Diet. p. 227. 

 Valvata branchialis, Gruithuisen (1821), Nov. Act. Nat. Cur. vol. x. 



p. 437. pi. xxxviii. f. 13. 

 Hab. Throughout Europe. Siberia. (Adhering to stones and submerged 



sticks, in tranquil and gently running waters.) 

 The name cristata given to this Valvata, refers to the branchial 

 plume, not to the shell, and, as may be seen by our list of synonyms, 

 it has been given by different authors to both species. V. cristata, 

 the subject of our vignette of the living animal, is much smaller 

 than V. piscinalis, and very much darker in colour'; while the shell 

 is constructed on a different plan, being formed of only three and 

 a half to four slowly enlarging whorls lodged one upon the other, 

 in a nearly discoidal manner, as in Planorbis glaber. 



The distribution of V. cristata is similar to that of V. piscinalis, 

 and it is represented in the same manner in the West Indies, by 

 V. fygme&a of Professor C. B. Adams. In habit it is also the same, 

 making active use while swimming, of its trunk and foot segments. 



Family III. NEEITACEA. 



Head produced into a short proboscis, eyes on short slender stalks detached 

 from the tentacles, branchice parallel, roimded plates set on a long tri- 

 angular membrane. Shell feio-iohorled, rather solid. 

 The Neritacea are a numerous group of mollusks, part marine, 



