84 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



Specimens examined.— Thirty-hiir from the following stations: 

 Specimens of Thrissacanthias penicillatus examined. 



Remarks. — This species was originally described under the genus Persephon- 

 aster, although I was uncertain of the identification at the time. The radically 

 difTerent arrangement of gonads wliich extend part way along the ray, on either 

 side, and the presence of a large actinal adambulacral spine are the two important 

 features which distinguish Thrissacanthias from Perse phonaster. 



Although the types of Perse phonaster and Psilasteropsis have a different facies, 

 an analysis of the characters of several species- from Hawaii, the Philippines, and 

 Japan seems to warrant uniting the two genera. Tj'pical Psilasteropsis has narrow 

 block-Uke inferomarginals which do not encroach far onto the actinal surface, 

 while in typical Persephonaster the inferomargmals are somewhat wader actinally 

 and the superomarginals possess stout spines. In other species of Persephonaster 

 tiie inferomarginals encroach conspicuously onto the actinal surface and the supero- 

 marginal spme is small. The arrangement of gonads, general character of adam- 

 bulacial armature, armature of inferomargmals, distribution of papulte, armature of 

 moutli plates (especially the angular marginal series and presence of two teeth at the 

 inner angle of jaw), and arrangement of actinal intermediate plates are the same 

 in the two genera. Persephonaster is the older name. (See also Koehler, 1909a.) 



Tritonaster is probably a specialized offshoot of Persephoyiaster, distinguished 

 by the unusually small superomarginals, tlie very tumid inferomarginals (defming 

 ambitus), and by the rudimentary actinal intermediate plates of the ray. 



Bhikiaster also resembles Persephonaster, but is distinguished hj the presence 

 of an odd interradial series of actinal intermediate plates, and lobed, imbricating, 

 low, convex tabulate abactinal plates, simulating paxill^. 



In Japanese waters there is a species, yet undescribed, wliich resembles penicil- 

 latus in general appearance, but dilfei-s in several important and many minor details. 

 This species has about three superomarginal spines in a transverse series; proximally 

 four or five inferomarginal spines with several auxiliary spinules; distally three; a 

 remarkable adambulacral annatnre consisting of a very angular furrow series of 

 three small spinelets set high in furrow (as in Ilenricia) the true margin l)eing occu- 

 pied by four or five spinelets belonging to the first actinal series. The remamder of 



