No 2. — TJie Starfishes of the Genus Heliaster. By Hubert 



Lyman Clark. 



The starfishes placed by Gray (1840) in the group to which he gave 

 the name Heliaster are of more than usual interest because of their 

 limited geographical distribution their exclusively littoral habitat, and 

 the large number of rays which they have. Moreover they appear to be 

 remarkably plastic and there has long been reason to believe that the 

 group contains several well-marked forms, limited to very circumscribed 

 geographical areas. As the collection of the Museum of Comparative 

 Zoology contains a large number of specimens from a dozen or more 

 different localities, it seemed worth while to make a careful study of the 

 group, especially with reference to three questions which have been 

 raised concerning it. (1). How many valid species of Heliaster are 

 there, what is their relation to each other, and what is the geographical 

 distribution of each 1 (2). With how many rays does Heliaster begin 

 its post-larval life, where and how do the new rays arise, in what order, 

 and with how much variability 1 (3). What is the relation of Heliaster 

 to Asterias and other starfishes, and by what systematic arrangement 

 can that relationship best be shown 1 In finding the answers to these 

 questions, we discover some important evidence on the subject of isolation 

 as a factor in the formation of new species. 



In addition to the material in the Museum collection, I am indebted 

 to Dr. W. K. Fisher, of Leland Stanford Junior University, for the loan 

 of material from the Galapagos Islands, belonging to the Museum of 

 that University, and to Dr. Eichard Rathbun, of the United States 

 National Museum, for much valuable material from the collections under 

 his care. To both of these gentlemen I herewith extend my sincerest 

 thanks. In all I have had, from at least 15 distinct localities, 346 

 specimens of Heliaster, ranging from 20 to 300 mm. in diameter. 



Historical. 



The following annotated bibliography gives a complete resume' of our 

 knowledge of Heliaster and its several species, from the first published 

 reference in 1767 down to July 1, 1906 : — 



