GEOGRAPHICAL DISTRIBUTION. 



147 



TABLE EXPRESSING THE RELATIONS BETWEEN THE DIFFER- 



ENCES IN STRUCTURE OF THE GASTROPODA AND 



DIFFERENT CONDITIONS OF ENVIRONMENT. 



Clossophora 



Class: I. Scaphopoda 



2. Placophora ^ 



3. Gastropoda 



4. Pteropoda 



Class Gastropoda. 



Order: I. Prosobranchia 



2. Heteropoda 



3. Opisthobranchia. . . . 



4. Pulmonata 



Order Prosobranchia. 



Suborder : a. Cyclobranchina. . 



b. Aspidobranchina. 



c. Cteiiobranchina. . 

 Suborder Ctenobraiichina . 



Section: i. Ptenoglossa 



2. Taenioglossa 



3. Rachioglossa 



4. Toxoglossa 



Section Tc^nioglossa. 



Div. I. Siphonostomata 



2. Holostomata 



Family: Cych'Stomidae 



Cyclophuridse 



Truncatellida£ . . .. 



Aciculidae 



Assimmeidae 



Paludinidae. . . ... 



Hvdrubiidae 



Valvatidse 



Melaniidae 



Littorinidae 



Rissoidae 



Cerithiidae , 



Naticidae 



Marine. 



( P 



( P 



( P 



el a 



el a 



el a 



Ma 



g 1 



g > 



c ) 



g 1 



c) 



rine& Fr 



Note. — The stars opposite the name of each group indicate the kind of 

 environment to which ihe genera of the group are adapted. 



Summary of Results. — This analysis of the distribution of 

 the various types of Gastropods may be summarized as follows : 



The organic structure of Gastropods is such that it is 

 capable of adjustment to all the conditions of environment 

 found inhabited by living things on the face of the earth, or 

 in the waters under the earth. 



