32 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



longiseries; pedicellariae of the straight sort only, the crossed being absent; spinelets 

 delicate and slender, usually in regular longiseries, sometimes absent; alternate 

 adambulacral plates (in one genus, all) with a prominent spiniferous projection into 



furrow 



Starfishes of the Zoroasteridae are abundant on muddy bottom in deep water 

 off the west coast of the United States, and form a very characteristic element of the 

 fauna. While the species are not numerous, individuals swarm m some localities, 

 judging by the results of dredge hauls. ^ 



Further study of Myxoderma, first proposed as a subgenus, has shown it to be 

 very distinct from Zoroaster. The capture of large examples of Cnemidaster wymlh 

 in the Gulf of Tomini, Celebes, not a great distance from the type-locality, has 

 thrown a new light upon a genus which was based upon a young and inadequate 



specimen. 



Mammaster is closely related to Cnemidaster. Clark (1920, p. 96) has found that 

 in Mammaster the first carinal plate, just distal to the primary radial is conspicuously 

 enlarged and is larger than the adjoining second marginals. Mammaster also lacks 

 adradial plates. The genus is monotypic and is found in the West Indies and Gulf 



of Mexico. 



Clark (1920, p. 100) has prepared a very useful synopsis of the species of 

 Zoroaster. This paper, furthermore, contains a good review of the family. 



SYNOPSIS 0.' THE KNOWN GENERA OF ZOROASTERIDAE 



o 1 . Dorsal surface not devoid of spines and not covered with a smooth tough membrance in sharp 



contrast to the spiniferous of squamiferous actinolateral regions. 



b>. Superambulacral plates absent, no conspicuous buttress extending from the upper enlarged 



end of the first two pairs of ambulacral plates to the body-wall at the interradial angle. 



e*. All adambulacral plates carinate on the furrow face. Genotype, Prognaster grimaldii 



Perrier Prognaster 10 Perrier. 



c 1 . Adambulacral plates alternately carinate and noncarinate. 



d l . Rays long, slender; disk small; abactinal, marginal, and actinolateral plates arranged 

 in regular longitudinal lines along ray, a series of adradial plates being always present; 

 all but the median radial or carinal, which are larger, form also transverse series; plates 

 are covered with small, papilliform, skin-covered spinelets, and most of them bear an 

 enlarged spine; papular areas generally very small but sometimes nearly as large as 

 plates; straight pedicellariae present; actinolateral plates in three to five series, the 

 upper subequal to the inferomarginal plates; superomarginal plates not conspicu- 

 ously larger than the inferomarginal plates. Genotype, Zoroaster fulgens Thomson. 



Zoroaster Thomson. 

 d 2 . Plates of ray arranged in regular longitudinal series, the carinal plates the largest; abac- 

 tinal and marginal plates armed with fairly large, skin-covered scales which mask 

 all plates except some of the disk-plates and the carinal series along ray; no pedi- 

 cellariae; actinolateral plates, in two or three series, much smaller than inferomargi- 

 nals; superomarginal plates much larger than inferomarginal plates. Genotype, 

 Pholidaster squa?natus Sladen Pholidaster Sladen. 



• Fisher, Bull. U. S. Nat. Mus., 100, vol. 3, 1919, p. 480.— Clark, Mem. Mus. Comp. Zool., vol. 39, No. 3, 1920, p. 97. 



io Prognaster Perrier, "Comptes rendus," vol. 112, 21, No. May 5, 1891, p. 1226. Type, P. grimaldii. Also "Resultats des 

 earnpagnes scientiflques du Prince de Monaco," fasc. 11, 1896, p. 22, pi. 2, figs. 1, la-b. In the meantime, Perrier described Prognaster 

 as a new genus with P. longicauda, new species, ostensibly as type (Eip6d. scientir. du "Travailleur" at du "Talisman," 1894, 

 p. 119). This species does not seem to be congeneric with grimaldii, which, o( course, is the genuine genotype. 



