CONTENTS 
Introduction, ........ 
Organisation op the Pteropoda, ..... 
I. Thecosomata, ....... 
A. Family I. Limacinidse, ..... 
B. Family II. Cavoliniidse, ..... 
C. Family III. Cymbuliidse, ..... 
D. Phylogenetic Relations of the Thecosomata among themselves, 
E. Summary on the Thecosomata, .... 
II. Gymnosomata, ....... 
A. Family I. Pneumonodermatidse, 
B. Family II. Clionopsidae, ..... 
C. Family III. Clionidse, ..... 
D. Family IV. Halopsychidse, .... 
E. Summary on the Gymnosomata, .... 
III. Summary on the Pteropoda, ..... 
Affinities and Phylogenetic Relationships of the Pteropoda, 
I. Historical, ....... 
II. Are the Pteropoda Cephalopoda 1 ... . 
III. Are the Pteropoda Gastropoda 1 .... 
IV. Special Affinities of the Thecosomata and Gymnosomata, 
A. Thecosomata, ...... 
B. Gymnosomata, . . . 
V. Do the Pteropoda constitute a Primitive or Derived Group ? 
VI. Polyphyletic Origin of the Pteropoda, .... 
A. Origin of the Thecosomata, .... 
B. Origin of the Gymnosomata, .... 
VII. Summary, ....... 
VIII. General Conclusions, . . , 
PAGE 
1 
5 
5 
5 
12 
21 
28 
37 
37 
38 
45 
47 
51 
55 
56 
57 
57 
60 
75 
77 
79 
82 
88 
89 
89 
94 
95 
95 
