CLARK: THE STARFISHES OF THE GENUS HELIASTER. 39 



second is not true of all Heliasters. The third, although quite characteristic, is 

 not confined to this genus. Accordingly, the following diagnosis of the genus, 

 which represents our present knowledge, does not differ markedly from that of 

 Gray:- 



Disc large, not set off externally from the fused bases of the rays, little elevated, 

 with reticulated abactinal skeleton, and more or less numerous spines, pedicellariae, 

 and papulae. Rays numerous, more than 20 in normal adults, more or less united 

 at base, so that only a relatively small part (15-70% )is free. 1 Adambulacral arma- 

 ture variable, usually single, sometimes double, especially near tip of ray ; spines 

 of alternate plates often of two sharply contrasted sizes, especially near base of 

 ray. Pedicels arranged in two more or less zigzag rows, so that near middle of 

 ray they are, as a rule, distinctly quadriserial. Forcipate and forficate pedi- 

 cellariae both present, the latter often of two quite distinct sizes. Interbrachial septa 

 double and well developed, expanding at inner (proximal) end and uniting laterally 

 more or less extensively, to form a discobrachial wall, so that the cavity of the 

 disc is almost completely separated from the cavities of the rays. (See plate 6, 

 fig. 1). 



This well-marked genus is easily distinguished by the number of rays alone, 

 from all other starfishes except Pycnopodia and Labidiaster. From the former 

 it is readily separated by the well-developed abactinal skeleton, the large disc and 

 the fused rays. From Labidiaster it differs in the fused rays and quadriserial 

 pedicels. The double interbrachial septa with the remarkable discobrachial wall 

 are internal features, distinguishing Heliaster from either genus. — The distribu- 

 tion of Heliaster is remarkably restricted as it occurs only in very shallow water 

 along the tropical and subtropical coasts of the eastern Pacific Ocean. I can find 

 no record of a specimen being taken with a dredge or trawl, so that they are 

 apparently littoral starfishes in the strictest sense of that term. They occur 

 upon and among rocks in the neighborhood of low-water mark. The most 

 northern point of their range, as shown by the specimens before me is San Luis 

 Gonzales Bay, Gulf of California, in latitude 29° 15' N., while the southern 

 extreme on the mainland appears to be in the vicinity of Valparaiso, 33° 2' S. lat. 

 There are no published records of the occurrence of Heliaster, either north or 

 south of these limits, and it is not recorded from any of the outlying islands, save 

 Juan Fernandez, 33° 38 ; S. lat., and the Galapagos, on the equator. — Nothing 

 has been recorded of the habits of Heliaster, but preserved specimens show that 

 the food consists very largely of small mussels, limpets, and acorn-shells (barna- 



1 In estimating the percentage of ray that is free, the length of the free portion 

 is divided by R. (i. e., the distance from centre of abactinal surface of disc to tip of 

 ray) as it is not feasible to measure the actual length of ray. Consequently the 

 free part is really a larger proportion of the ray itself than the percentages herein 

 given would seem to indicate. It should also be noted that the rays are fused to 

 a much greater extent relatively in adult than in young specimens ; very young 

 individuals often have twice as much free ray as adults of the same species. 



