THE 
VOYAGE OP H.M.S. CHALLENGER. 
ZOOLOGY. 
REPORT on the Pteropoda collected by H.M.S. Challenger during the 
Years 1873-76. By Paul Pelseneer, D.Sc. (Brussels). 
K'a.c/ x\ 
PART H.-The THECOSOMATA. 
INTRODUCTION. 
About the end of the year 1885 I was entrusted with the task of making a systematic 
and descriptive Report on the Gymnosomatous Pteropods and an anatomical one on the 
entire order, and in the beginning of the present year (1887) the entire Report on the 
Pteropods was entrusted to me for completion. 
The Report is thus divided into three portions as follows : — 
1. The systematic survey of the Gymnosomata, which has been already published. 1 
2. The present Report on the Thecosomata, which along with the former includes the 
entire systematic survey of the Pteropods collected on the Challenger Expedition. 
3. The anatomy of the Thecosomata and Gymnosomata. 
As with the Gymnosomata, so in regard to the Thecosomata, I have been forced to make 
a monographic study of the entire subgroup. But I have not here described all the species 
actually known, partly because they are on the whole more familiar than the Gymnosomata, 
and partly because the delay which has been involved in the completion of the entire 
Report made such a survey impossible. I shall therefore restrict myself to an enumeration 
of the indubitably genuine species among the entire list of those hitherto described, and 
to synoptic tables in which these are distinguished from one another. 
1 Zool. Chall. Exp., part lviii. 
(ZOOL. CHALL. EXP. — PART LXV. — 1887 .) 
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