104 DISTRIBUTION OF ANIMALS. [PART I. 
MOLLUSCA. 
The Mollusca are usually divided into five classes as 
follows :— 
Classes. 
I. Cephalopoda ... ... Cuttle-fish. 
II. Gasteropoda ... ... Snails and aquatic Univalves. 
III. Pteropoda w+. «ee Oceanic Snails. 
IV. Brachiopoda ... ... Symmetrical Bivalves. 
V. Conchifera  ... ... 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 followed is that of Dr. Pfeiffer for the 
Operculata and Dr. Von Martens for the Helicide. The 
families chiefly referred to are :— 
Class II.—GASTEROPODA. 
Order 2.—Pulmonifera. 
Fam. 
. Helicide. 
Limacide. 
Oncidiadee. 
Limnezide. 
Auriculide. 
. Aciculide. 
. Diplommatinide. 
. Cyclostomide. 
. Helicinide. 
In-operculata 
C2 COMI OB Bw DO 
Operculata ... 
me 
