REPORT ON THE ASTEROIDEA. 561 



This large and widely distributed genus was subjected a few years ago to a critical 

 revision by Professor F. Jeffrey Bell/ who carefully investigated the claims of the large 

 number of forms referred to .Aster ias to be ranked as distinct species. All workers at the 

 group owe a debt of gratitude to the author of this admirable and useful memoir. Pro- 

 fessor Bell divided the genus into artificial sections, and systematised the recognised species 

 by means of easily observed characters, which will afford great help in the determination 

 of specimens. 



The number and the great variety of the species of Asterias make the genus a very 

 difficult one to deal with, and its subdivision into natural groups has been a long felt 

 desideratum. Professor Bell's scheme is, however, essentially a systematic key, mainly 

 artificial in character, rather than a natural arrangement by affinities ; it not unfre- 

 quently results that species which are nearly related, and present a close similarity of 

 habit, are widely separated and placed in sections wherein they stand isolated. For a table 

 of specific differences, this perhaps may in some cases be an advantage, though it is 

 decidedly unnatural from a taxonomic point of view. 



Whilst fully recognising the excellence and utility of Bell's classification, I venture to 

 think that the two methods — the artificial and the natural — may advantageously be com- 

 bined, and for the species with which the present Report is concerned, I have formulated 

 a scheme which seems to fulfil these requirements. To discuss the partition of all the 

 species of Asterias would demand more space than I should be justified in occupying in this 

 place, and would introduce too large an amount of matter foreign to the Challenger Report. 



The groups or alliances of species which I have proposed, may, in my opinion, be 

 regarded as of subgeneric rank. I further believe that some of them may ultimately stand 

 as independent genera, but until more is known of the special anatomy of the species, I 

 refrain from so classifying them. 



Synopsis of the Species of Asterias herein mentioned. 



A. Asterias rubens group : Abactinal spinelets numerous, but not arranged in 

 definite order, usually small and often more or less grouped. Papula? 

 numerous, in groups ......... Asterias. 



a. Heteractinid : Having six rays. 



a. Diplacanthid : Armature of the adambulacral plates consist- 

 ing of two spines. 

 a. Rays long and tapering, spinulation characteristically 

 vesiculated. No spinelets between the parambul- 

 acral series of papulae ....... vesiculosa. 



/5. Rays much shorter and less tapering. Spinulation not 

 specially vesiculated. Occasional spinelets between 

 the parambulacral series of papula? .... meridionalis. 



1 Troc. Zoul. Soc. Land., 1881, pp. 492-515. 



(ZOOL, CHAIX. EXP. — FAUT LI. — 1888.) 71 



