GASTEROPODA. 



209 



Some of the gasteropoda can suspend themselves by glutinous 

 threads, like litiopa and Bissoa parva, which anchor themselves 

 to sea-weeds (Gray), and cerithidae (Fig. 75), £- 

 ■which frequently leaves its proper element, 

 and is found hanging in the air. (Adams.) A 

 West India land- snail [cydostoma suspensum) 

 also suspends itself. (Guilding.) The origin 

 ■^ these threads has not been explained ; but 

 some of the limaccs lower themselves to the 

 ground by a thread which is not secreted by 

 any particular gland, but derived from the 

 exudation over the general surface of the body. 

 (Lister, D'Orbigny.) 



The division of this extensive class into 

 orders and families has engaged the attention 

 of many naturalists, and a variety of methods 

 have been proposed. Cuvier's classification was Fig- 75. 



the first that possessed much merit, and several of his orders 

 have since been united with advantage. 



System of Cuvier. System now adopted. 



Class. Gasteropoda. 

 Order 1. Pectinibranchiata n 



l CydoW^ [ ^^^^- Prosohranchiata, M. Edw, 



4. Tubulibranchiata -^ 



5. Pulmonata 



6. Tectibranchiata ^ 



7. Inferobranchiata 



8. Nudibranchiata. 



Ord. Pulmonifera. 



Ord. OpisthohrancMata, M. Edw. 



Class. Heteeopoda. 



Ord. Nudeolranchiata, Bl. 



Order I. Prosobraj^chiata. 



Abdomen well developed and protected by a shell, into which 

 the whole animal can usually retire. Mantle forming a vaulted 

 chamber over the back of the head, in which are placed the 

 excretory orifices, and in which the branchiae are almost always 

 lodged. Branchioe pectinated, or plume-like, situated (proson) 

 in advance of the heart. Sexes distinct. (M. Edwards.) 



Section A. Siphonostomata. Carnivorous Gasteropods. 



Shell spiral, usually imperforate; aperture notched or produced 

 into a canal in front. Operculum horny, lamellar. 



