Ii6 A Guide to the Zoological Collections in the 



vast number of marine forms : it is divided by Professor 

 Ray Lankester into two sections— a larger section, knovi^n 

 as Reptantia or Creepers, in which the foot forms a disk 

 for crawling ; and a very much smaller section, known as 

 Natantia or Swimmers, in which a part of the foot forms 

 a fin-like swimming organ. 



REPTANTIA. 

 There are three sub-Orders of crawling Azygobranch 

 Mollusks, namely, (i) the fiolochlamyda, in which the 

 free edge of the mantle is simple or very slightly produced, 

 and the lip of the shell therefore unnotched or only 

 slightly notched ; (2) the Pneumochlamyda, in which the 

 mantle-chamber forms a lung-sack, as it does in the 

 Snails, with which, however, they must not be confused ; 

 and (3) the Siphonochlamyda, in which the edge of the 

 mantle forms a long tube or siphon which notches deeply 

 the lip of the shell. 



a, GASTROPODA AZYGOBRANCHIA HOLOCHLAMYDA. 



[aia0£0l29(E-l48Jl]. 



Lip of shell not channelled, or only slightly so [Ceri- 

 thiidse). The animals are mostly vegetarian: many live 

 in the sea, many in salt and brackish swamps, some in 

 freshwater, and some on dry land. They are grouped 

 by Professor Ray Lankester into 19 families, 18 of which 

 are thoroughly well represented in the exhibited collection. 



1st Family, Trochidae [Cases 129C 132C]. 



This is a very large Family of marine gastropods^ the 

 species of which are commonly found not far from low- 

 water mark. They feed principally on sea-weed, and are 

 universally distributed. A few species live in the depths 

 of the ocean. The shells are mostly pyramidal or turbinate, 

 and are furnished with an operculum which may be either 

 stony or horny. Most of the genera of this large family 

 are represented in Cases i2gC — 132C. 



2nd Family, Neritidse [Cases 133 A — 134A]. 



