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] (3). What is the relation of Heliaster to Asterias and other starfishes, and by what systematic arrangement can that relationship best be shown? 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. Richard 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 : —
BioStor
