38 bulletin: museum of comparative zoology. 



National Museum, Rathbun (1887) has shown beyond question the 

 existence of at least four well-marked species, and the present investiga- 

 tion confirms his conclusion. But Rathbun had no material from Juan 

 Fernandez, and consequently does not refer to canopus Perrier, while he 

 had only a few specimens from the Galapagos, and these he naturally 

 assigns to the species named by Gray, which came from Hood's Island. 

 The material now available, includes a fine series of adults and young 

 from Juan Fernandez, which confirms Perrier's opinion that the species 

 occurring at the island is quite different from helianthus and is entitled 

 to recognition as a distinct species, canopus. The number of specimens 

 from the Galapagos makes it possible to show that the Heliasters of that 

 group of islands present certain characters in which they are obviously and 

 apparently constantly different from their nearest allies on the American 

 coast. Of course there is room for difference of opinion as to whether 

 these characters 'are sufficiently tangible and constant to warrant calling 

 the island forms separate species, but since the characters are associated 

 with sharply distinct geographical areas (for Heliaster is littoral in the 

 extreme) and since the island forms were long ago named by Gray, and 

 one of the mainland near allies by Xantus, it seems better to give the 

 other mainland ally a name, and thus recognize seven species of Heli- 

 aster. In no other way can the apparent plasticity of the genus and 

 the results of isolation be so well brought out. 



Heliaster Gray. 



Asterias; section e, Heliaster Gray, 1840. Ann. Mag. Nat. Hist., 6, p. 179. 

 Heliaster (used without comment as a generic name) Xantus, 1860. Proc. Acad. 

 Nat. Sci. Phil., p. 568. 



Heliaster Dujardin et Hupe', 1862. Hist. Nat. Zoo.ph. Echin., p. 343. 

 Asterias ; section f, Heliaster Gray, 1866. Syn. Starf. Brit. Mus., p. 2. 

 Heliaster Perrier, 1875. Arch. Zool. Exp., 4, p. 299. 



Since Perrier's diagnosis the genus Heliaster Gray has been universally 

 recognized. 



Gray's diagnosis was as follows : — 



Body discoidal, divided at the edge into numerous short tapering rays ; the series 

 of spines near the ambulacral series rather crowded, large, and elongated. 



To this characterization, Perrier added nothing, but Viguier (1878) suggested 

 as additional features the funnel-shaped depression in which the mouth is placed, 

 the fragmentation of the madreporite, the double iuterbracliial walls, and the 

 fused condition of that interradial plate which he calls the " odontophore." 

 Unfortunately the first and last of these characters are of doubtful value, and the 



