CONTENTS. 
PAGB 
Introduction, ............ 1 
Habits of the Thecosomatuus Pteropods, ........ 3 
The Thecosomata of the Challenger Expedition, ....... 3 
Description of Genera and Species, ........ 5 
The Genera and Families of Thecosomata, ........ 5 
Family I. Limacinidae, ......... 9 
Limacina, . . . . . . . . . .15 
Peraclis, .......... 32 
Appendix to Limacinidae, . . . . . . .37 
Family II. Cavoliniidae, ......... 41 
Clio , ........... 42 
Cuvierina , .......... 66 
Cavolinia, . . . . . . . . . .69 
Family III. Cymbuliidae, ......... 92 
Cymbulia , .......... 96 
Cyrnbuliopsis, . . . . . . . . . .100 
Gleba, ........... 101 
Summary, ............ 105 
Geographical Distribution, . . . . . . . .107 
A. List of Stations, . . . . . . . . . .107 
1. Stations at which the Living Specimens were collected by trawling and dredging, . 107 
2. Principal Stations at which Shells of Thecosomata were obtained from the Deposits, . 116 
B. Geographical Distribution of the Genera, . . . . . . .121 
C. The Species of Thecosomata arranged in Provinces, . . . . .123 
Alphabetical Index, . . . . . . . . . .129 
Explanation of Plates. 
