104 



DISTRIBUTION OF ANIMALS. 



[fart I. 



MOLLUSCA. 



The Mollusca are usually divided into five classes as 

 follows : — 



Classes. 

 I. Cephalojaoda 

 II. Gasteropoda 



III. Pteropoda 



IV. Brachiopoda 

 V. Conchifera 



Cuttle-fish. 



Snails and aquatic Univalves. 

 Oceanic Snails. 

 Symmetrical Bivalves. 

 Unsymmetrical Bivalves. 



The Gasteropoda and Conchifera alone contain land and 

 freshwater forms, and to these we shall chiefly confine our 

 illustrations of the geographical distribution of the Mollusca. 

 The classification folloM^ed is that of Dr. Pfeiffer for the 

 Operculata and Dr. Von Martens for the Helicidse. The 

 families chiefly referred to are : — 



In-operculata 



Operculata ... 



Class II.— GASTEROPODA. 



Order 2. — Pulmonifera. 

 Fain. 



1. Helicidse. 



2. Limacidae. 

 r$. Oncidiadse. 



4. Limnasidse. 



5. Auriculidse. 



6. Aciculidae. 



7. Diplomiuatinidse. 



8. Cyclostomidae. 



9. Helicinidae. 



