ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 127 



contain only about thirty pores, whereas in the latter race there are seldom as 

 few as forty in an equally large specimen. However, Ludwig recortls and figures 

 a papularium with fift\' papula? (R = 65 mm.) in agassizi. There are more numerous 

 actinal pcdiccllariiB in evoplus, and m agassizi, as already recorded, no abactinal or 

 intermarginal jiedicellariae. In other characters the two species are practically 

 alike. 'Whatever slight difTcrences in spine length and counts one might mention 

 is more than compensated for by the indivitlual variation in evoplus. 



It will not be surprising if mimicus, fillioli, agassizi, and evoplus are nothing 

 more than races of one witlely distributed species. They are all very closely 

 related. 



Genus LUIDIASTER Sluder. 



Luidiasler Studer, Sitzungsber. naturforsch. Freunde, Berlin, Oct. 16, 1883, p. 131. Type, 

 L. hirsiilKS Studer. — Ludwig, Sitzungsber. k. preusa. Akad. "Wiss., vol. 23, 1910, p. 451. 



Acantharchaster V.errill, Proc. U. S. Nat. Mus., vol. 17, 1894, p. 268. Type, Arckaster dawsoni 

 Verrill.— Fisher, Zool. Anz., vol. 35, March 29, 1910, p. 549. 



Cheiraster Perkier (part), E.\p6d. sci. du Travailleur et du Talisman, 1894, p. 275. — Fisher 

 (part), Bull. U. S. Fish Comm. for 1903, ph. 3, 1906, p. 1042. 



Diagnosis. — Benthopectinidiis without odd interradial marginals and with the 

 abactinal plates a simple form of low paxillie, bearing a prominent central spine, 

 surrounded by accessory spinules; these interspersed with secondary smaller plates, 

 usually without central spine, bearing instead a few spinelets of var3-ing length, 

 always short on outer part of ray; papuI;B not sharply circumscribed, but occupjing 

 entire basal part of rays, and adjacent portion of disk, and distal part of area more 

 or less two-lobed; peilicellarise pectinate, occupying two plates and occurring on 

 abactinal surface, sometimes also on actinal intermediate and marginal plates; 

 actinal intermetliate jplates few, spinous; marginal plates more or less alternate, 

 very spiny; adambulacral plates with saHent inner angle, and bearing a divergent 

 group of furrow spinules and a transverse actinal row of two or more long spines. 

 Dorsal muscle bands attached proximally to a crest of one or two ambulacral plates, 

 as well as to adjacent superomarginals. 



RcmarliS. — In this genus the primary abactinal plates of the papular region are 

 roundish vath faint imlication of lobing. The plates are raised into a low tabulum 

 bearing a variable number of spinules and a central movable spine. 



Tliis group (lifTers from Cheiraster, its nearest relative, in having the dorsal 

 muscle bands attached proximally to a special crest of an ambulaci'al ossicle, near 

 the point where the latter abuts against the superomarginal. The muscle is attached 

 also to the abactinal plates and superomarginals by the same tendon but the origin 

 is on an ambulacral plate. In Cheiraster inops and C. snyderi the attachment to 

 the ambulacral is wanting. In Chfiraster the papularium is more definitel}' circum- 

 scribed. In L. dawsoni the papulae extend all the way across the ray and occupy 

 the radial portions of tlisk, except at the very center. 



Ludwig includes five species: dawsoni, hirsutus, teres, vincenti, and gerlachei. 

 To these I would adil horri<lus, described by me as a Cheiraster in 1906. The test 

 as to W'hether all these are really congeneric will be the determination in each form 

 of the moile of attachment of tlie dorsal musi'le bands. I do not think gerlachei 

 is congeneric with dawsoni, and I am skeptical also concerning teres and vincenti. 

 I do not think oxijacanthus is synonymous with dawsoni, as Luilwig states. 



