THE 



VOYAGE OF H.M.S. CHALLENGEE. 



ZOOLOGY. 



REPORT on the Echinoidea/ dredged by H.M.S. Challenger during the 

 Years 1873-1876. Bv Alexander Agassiz. 



INTRODUCTION. 



In preparing this Eeport on the Challenger Echinoidea, I have purposely limited myself 

 to such topics as seemed most germane to the object of the Challenger Expedition, viz., 

 the careful systematic description of the species collected, and a detailed comparison in 

 all directions which promised to shed any light on the characteristics of the Echinid fauna 

 of the depths of the sea. 



A careful comparative study of the new species collected by the "Challenger" and by 

 the " Blake," seems to make a short revision of some of the principal lines of afBnities 

 of the recent and fossil Echinids desirable; as from our present knowledge of the affinity 

 of the Echinoidea several groups formerly considered somewhat aberrant can now be 

 shown to be closely connected. New and most unexpected systematic views have in 

 many cases been suggested by this comparative study of the striking deep-sea genera. 

 This comparison is the more interesting, as it brings out more prominently than could 

 otherwise have been done the genetic succession which undoubtedly exists between 

 the types still found living at great depths, and other genera characteristic of tlie 

 Cretaceous and Tertiary periods. 



There remains much to be done in the minute anatomy, not only of the new deep- 

 sea types but of the whole group of Echinoidea. We know as yet practically nothing 

 of the histology of the principal families ; for this reason I have not attempted a 

 more detailed examination of the Challenger Echinids, interesting and instructive as 

 it undoubtedly would have been, since there existed no terms of comparison in the 

 other groups. To have attempted to carry out such a comparative scheme for the 



1 It has beeu foiuid impracticable to incorporate in this Report publications on the Echinoidea which have 

 appeared during the wnnter of 1879-80 and subsequently. 



CS /; (ZOOL. CHALL. EXP. PART IX. 1881.) I 1 



