84 THE LAND AND FRESHWATER MOLLUSCA OP DORSETSHIRE. 



2. F. VIVIPAEA, Linn.) pi. 6. 



HELIX VIVIPARA, F. and H. iii., p. 11, pi. Ixxi., f. 14, 15. 



HELIX COMPACTILIS, Pult. cat,, p. 48. Penn. Brit. Zool. ed. iv., 

 pi. 85, top fig. 



Shell oval, rather ventricose, not so glossy as the last, yellowish- 

 green, with similar bands and striae ; whorls six and a half, convex, 

 the last occupying more than half of the shell ; the summit of the 

 spire not so sharply pointed as the other species ; suture rather deep ; 

 mouth oval; outer and inner lips form a complete peristome ; 

 umbilicus very narrow, merely a chink; operculum slightly concave, 

 rather thick, glossy, marked with distinct concentric striae; the 

 centre nearest Ithe inner lip. L.1.5. B.I. 2. 



Hab. Similar to that of the last species. This is Pulteney's 

 H. compactilis, which he identifies by Pennant's figure, and is 

 unquestionably P. vivipara ; it is denominated by Pulteney as the 

 Round Three-banded Snail. Rackett leaves it out in his edition 

 of Pulteney's Catalogue. 



Genus IL BYTHINIA (BITHINIAJ, Gray. 



Differs from the preceding genus in being oviparous instead of 

 ovoviviparous and the operculum testaceous instead of being horny ; 

 umbilicus small or hidden. 



1. BYTHINIA TENTACULATA, IAnn.> pi. 6. 



HELIX TENTACULATA, Pult. cat., p. 49, Rack, ed., p. 56, pi. 21, 



f. 12. 

 Body dark brown, or almost black above. 



Shell sub-conical or oval, rather slender, glossy, smooth, brown 

 amber-colour, with fine, unequal longitudinal striae ; whorls six, the 

 last comprising nearly two-thirds of the whole shell, ventricose ; 

 a rib, which is sometimes white, strengthens the interior of the 

 outer lip which forms a continuous peristome with the inner Up; 

 umbilicus merely a chink ; operculum obliquely oval, angular above, 

 and slightly concave. L.0.5. B.0.25. 



Hab. Ditches, brooks, canals, and rivers ; usually attached 

 to aquatic plants. Quaternary tufaceous deposit at Blashen\vell, 

 Kingston; Purbeck (J.C.M.P.j. 



