CLASSIFICATION OF GASTEROPODA 



CHAP. 



Thus we have 



MOLLUSCA 



Glossophora 



Cephalopoda Gasteropoda Scaphopoda 



Aglossa 



Pelecypoda 



Classification of Gasteropoda. — The G-asteropoda are nu- 

 merically very largely in excess of the two other Orders of the 

 Glossophora, far more complicated as regards classification, and 

 contain a large proportion of those examples of the Mollusca 

 which are most familiar to the ordinary observer. It will there- 

 fore be convenient to postpone for the present a fuller discussion 

 of the subdivisions of the Cephalopoda and Scaphopoda, as well 

 as of the Aglossa, returning to them again in special chapters 

 (chaps, xiii. and xvi.), and to devote a few introductory words 

 to the classification and relations of the Gasteropoda. 



The Gasteropoda are divided into four Classes, AmpJiineura^ 

 Prosohranchiata^ Opisthobranchiata^ and Pulmonata. 



(1) The Amphineiira^ are bilaterally symmetrical Mollusca, 



Tfli^. 



Fig. 3. — An example of the 

 Aplacophora, Neoinenia ca- 

 rinata Tullb.: a, anus; gr^ 

 ventral groove; m, mouth. 



Fig. 2. — An example of the 

 Polyplacophora : Chiton spin- 

 osus Brug. 



I.e. with organs either single and central, or paired and disposed 



The shell, when 



Some authorities regard the 



on either side of the longer axis of the animal. 



1 dfxcpl, on both sides ; vevpov, nerve, vessel. 

 Amphineura as a distinct Order. 



