PULMONOBRANCHIA TA. 33 



Var. 3. acuminata. Spire still more produced and ending in 

 a rather sharp point. Avon River, Bristol (J. G. J.), North of 

 Ireland (Mrs. Puxley), B.C., vol. i. p. 73. 



Monst. sinistrorsa. " Sunbury (Groves)," Gwyn Jeffreys, 

 * Annals and Magazine of Nat. Hist.,' Nov. 1878, p. 382. 



2. V. CRISTA'TA,* MULLER. PL. IV. 



Body dark brown or greyish above, slaty-grey below ; ten- 

 tacles filiform, close together, very slightly pointed, but recurved 

 at their tips ; eyes small, round, black ; snout rather narrow, 

 curved, very convex above, broad in front, wrinkles indistinct ; 

 mouth narrow, nearly straight ; branchial plume transparent, 

 with about fifteen filaments on each side of the stalk ; branchial 

 appendage shorter than the tentacles ; foot entirely separated 

 from the snout, deeply cleft in front, greyish-brown, tail broad, 

 keeled below. 



Shell discoid, flat above, concave beneath, rather solid, slightly 

 transparent, pale horn-colour, with close-set striae in the line of 

 growth ; epidermis thin ; whorls 3-5, body whorl occupying at 

 least two-thirds of the shell ; spire slightly concave ; mouth 

 round ; outer lip thin, slightly reflected ; inner lip separated 

 from the base of the penultimate whorl, continuous with the other 

 lip ; umbilicus large ; operculum round, hollow, spire with about 

 twelve volutions, their outer margins forming projecting ridges. 



Inhabits the same situations as the last species, 

 from which it may be easily distinguished by the 

 flatness of its shell, which in this respect resembles 

 that oiPlanorbis. It is an inactive and timid mollusc. 



ORDER II. PULMONOBRANCHIATA.f 



Respiratory apparatus chiefly consisting of a network of delicate 

 vessels seated within a fold of the mantle and adapted for the 

 respiration of atmospheric air ; in those cases in which aquatic 



* Crested (in allusion to the branchial plume). 

 t Provided with a gill resembling a lung. 



