STAEPISHES OF THE PHILIPPINE SEAS. 447 



a straight series. S. subarcuatus Slaclen has fewer inferomarginal 

 spines (10-12), fewer furrow spines (3 or 4), and fewer oral and 

 suboral spines. The species is said to resemble S. endeca, which 

 S. tropicus does not. 



Genus CROSSASTER Mullet and Troschel. 



Crossastcr Muller aud Troschel, lS40a, p. 103. Type, Asterias papposa 

 Linnaeus. 

 The two genera, Solaster and Crossaster, have been united by 

 most recent writers,^ although in practice it is not very difficult to 

 recognize them. Since new species of the Crossaster type are con- 

 tinually being described, it is becoming more and more desirable to 

 keep them separate. A good differential character is the presence 

 in Crossaster of a complete membraneous interbrachial septum be- 

 tween the internal interradial calcareous dorsoventral pillar and 

 the margin. The pillar arises from the mouth plates and passes 

 upward, its point of union with the abactinal skeleton being usually 

 marked by a smooth spineless area. In Crossaster papposus be- 

 tween this calcified buttress and the margin there is a definite 

 septum separating the gonads of adjacent rays, while in Solaster en- 

 deca^ S. horealis^ and S. ahyssorum the pillar is present, but not the 

 membranous septum; as a result the gonads of adjacent rays are 

 not separated, and the coelom is continuous.- 



CROSSASTER SCOTOPHILUS (Fisher). 



Plate 124, fig. 1 ; plate 133, figs. 3, So. 



Solaster scotophilus Fisher, 1913c, p. 222. 



Diagnosis. — Related to Crossaster 2}cepposus, but differing in being 

 of a much more delicate habit, with more numerous furrow and sub- 

 oral spines, smaller paxillae, smaller and more numerous marginal 

 paxillae, and a much more delicate skeleton. Rays 9; R=48 mm., 

 r=14 mm., R=:3.4 r; breadth of ray at base 10 mm.; disk large, 

 rays slender, flexible, tapering to a sharp point; skeleton delicate, 

 open, irregular; paxillae small, the pedicel about 0.5 mm. high and 

 the longest spinelets 1.25 mm. long; marginal paxillae 24 or 25, deli- 

 cate; furrow spines very delicate, 8 or 9; subambulacral spines 7 to 9; 

 marginal mouth spines, 15. 



Description. — Abactinal skeleton very open with widely spaced 

 pseudopaxillae consisting of a low pedicel and ordinarily 15 to 25 

 very slender and sharp glassy spinelets, short about the periphery of 

 tabulum and increasing in length to the center where they are 3 or 



1 For some of the reasons for uniting them see Fisher, Wild, p. 389. Professor Ver- 

 rill, 1914a, p. 259, recognizes Crossaster and remarks that " the dorsal ossicles do not 

 form definite, oblique, transverse rows on tlie sides of the rays as they do in Solaster." 



2 Fisher, 1916a, p. 5. 



