GASTEROPODA. 107 



to the axis of the shell; having the margins disunited by 

 the projection of the last volution. The Helices, or Snails, 

 which are very numerous, and present considerable differ- 

 ences in the form of the shell, have by several more recent 

 authors been arranged into various subgenera. 



Helix arhustoriim The Grove Helix. Plate XIII. 



fig. 27. Subglobular, subumbilicated, finely striated longi- 

 tudinally ; greenish-yellow or reddish, beautifully mottled, 

 and streaked with reddish-brown, and a broad brown band 

 running throughout the middle of the volutions. One inch 

 in diameter. Inhabits the thickets and woods of Europe. 



OPtLER lY -GASTEROPODA. 



Animals with straight bodies, and never spiral, nor en- 

 veloped entirely in a shell, having a foot or muscular disk 

 under the abdomen, attached to the body nearly its whole 

 length, and serving for progressive motion. 



Section I — Pneumobranchi^. 



Branchiae constructed like a vascular net, on the wall 

 of a particular cavity, opening by a perforation which the 

 animal has the power of contracting and dilating at pleasure. 

 They respire air. 



TRIBE I. LTMACINEA. 



The animals almost wholly naked, with elongated bodies ; 

 and creeping by means of a ventral disk ; branchiae in the 

 form of a vascular network, lining a cavity, of which the 

 aperture is a hole capable of being contracted or dilated at 

 will. 



Gtniis 1.— VITRIN A.— Zawarc^J. 



Generic Character. — Body creeping, elongated, enail- 

 shaped, nearly straight ; posteriorly separated from the foot, 



