ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER 33 



6 J . Superambulacral plates present; a conspicuous buttress, the specialized first superambulacral 

 plate connects the upper end of the first two ambulacral plates with the bodywall at 

 interradial angle. 

 c 1 . Adradial plates present; two series of papular areas between the carinal and superomarginal 

 plates, the latter never conspicuously enlarged nor overlapping the carinals. Geno- 

 type, Zoroaster sacculatus Fisher Myxoderma Fisher- 



c*. No adradial plates; one series of very small adradial papular pores; superomarginal plates 

 of two sizes, alternately larger and smaller, overlapping the carinals strongly and 

 dominating these plates, which are sunken below the level of the superomarginals. 



Genotype, Bythiolophus acanthinus Fisher Bythiolophus " Fisher. 



a 1 . Abactinal plates of disk, the carinals, adradials (when present), marginals, and sometimes one 

 series of actinolateral plates devoid of spines or any conspicuous armature, but mostly 

 smooth and covered with a tough membrane of variable thickness, often partly obscuring 

 the plates; two to four lower series of actinolateral plates covered with squamiform fleshy 

 spinelets and sometimes a conspicuous appressed spine; superambulacral plates present, 

 the first conspicuously enlarged into a buttress connecting the upper end of the first two 

 ambulacral ossicles with the body wall. 



6 1 . With a series of adradial plates more or less well developed; first carinal scarcely or not at all 



larger than the first marginals which are evidently larger than the second; four or five 

 series of actinolateral plates. Genotype, Cnemidaster wyvilli Sladen- Cnemidaster Sladen. 



6 2 . Adradial plates absent, the inner lobe of the superomarginal plates overlapping the carinal 



plates; first carinal plate, just distad to primary radial, conspicuously enlarged, larger 

 than the adjoining second marginals which are very much larger than the first ones; 

 three series of actinolateral plates with rudimentary fourth series in large specimens. 

 Genotype, Zoroaster sigsbeei Perrier Mammaster Perrier. 



Genus ZOROASTER Wy villi- Thomson 



Zoroaster Wyville Thomson, The Depths of the Sea, 1873, p. 154. Type, Z.fulgens Thomson. 

 For key to species: Clark, Mem. Mus. Comp. Zool., vol. 39, No. 3, 1920, p. 100. 



Diagnosis. — Zoroasteridae lacking superambulacral plates, with small disk, com- 

 posed chiefly of primary apical plates, and long slender rays made up of a carinal series 

 of four to six lobed plates, overlapping on either side a regular adradial series, these 

 followed by two regular series of four-lobed or lozenge-shaped marginals and three 

 or four series of subsimilar actinolateral plates, imbricating so that the lower and the 

 adoral margins, or lobes, are free and overlap the aboral and upper margins of neighbor- 

 ing plates; adradials, marginals and actinolaterals also forming transverse series; 

 most of the plates normally with a central spine, and spinelets; papular areas very 

 small, in the junction between four plates; adambulacral plates short, band-like, 

 of two sorts: (1) prominent plates projecting into furrow forming a sort of carina 

 bearing a transverse series of three to six spines, the inner one or two frequently 

 bearing pedicellariae, sometimes quite large; (2) alternating with these prominent 

 plates are much narrower noncarinate plates bearing one or two transverse series of 

 two spines each, or a group of three with or more often without pedicellariae; pedi- 

 cellariae usually present on abactional and lateral plates; tube feet in four series 



H Proc. Biol. Soc, Washington, vol. 219, 1916, p. 31. Bull. U. S. Nat. Mus. 100, vol.3, 1919, p. 484, pi. 135, flgs. 1, la-c,- pi. 139 

 flgs. 1,2. In the description adradial plates should read superomarginal. The corrected diagnosis Is as follows: In general structure 

 resembling Zoroaster, eicept in the absence of adradial plates; in presence of superambulacral plates; In the specialization of the 

 first superambulacral plate as a conspicuous buttress running from the body wall at the interradius to the upper end of the first 

 ambulacral ossicle, and in the arrangement of the abactinal skeleton. The superomarginal series is more prominent than the carinal 

 consisting of alternately larger and smaller, transversely elongated plates, the larger of which overlie the lateral third of the carinals : 

 both sorts strongly overlap the upper end of the inferomarginals. Two series of marginal and five series of actinolateral plates. 

 Adambulacral plates as in Zoroaster. 



