453 



fometimes even inclined to convexity: but a mofl; efTen- 

 tial chara61er is, that the volutions taper more fuddenly 

 to the centre, terminating in a fmailer, but deeper um- 

 bilicus. The aperture is alfo more compreffed, and the 

 continuation of the carina within the mouth more con- 

 fpicuous. This flieil is not near fo common as the co7n- 

 planata, but is fometimes found in the fame waters. 



We firft difcovered it in the river Avo7i about Lack- 

 ham in Wiltjhire,hn\. all dead and bleached white; which 

 feems to be the charafler of this fhell in that Rate. We 

 do not, however, believe they inhabit that river, but 

 are brought into it in the time of floods: though we 

 could never find it elfewhere, amongfl the other fpecies, 

 which is common in that neighbourhood. We after- 

 wards found it near Wareham in Dorfetjliirc, where it is 

 not uncommon in the meadows clofe to that town, in the 

 ifle o^ Purbeck, in ditches and water courfes ; in company 

 with the complanata. Thefe were covered with a dufls^y- 

 green epidermis when alive. It is, doubtlefs, found in 

 other places, as we have feen it in feveral cabinets of 

 Englijh fliells, mixed, and confounded with the compla- 

 nata, under the title of Helix Planorbis, 



Animal pale, of a yellowifh tinge, with two long, 

 (lender, fetaceous tentacula ; with the eyes placed at 

 their bafe, beneath. Differs from the animal o^ H. com- 

 planata in the tentacula being fomewhat longer, and 

 particularly in their being pellucid yellow, and not 

 darker in the middle. 



Helix 



