North Pacific Zoroasteride. 
c'. Adradial plates present ; two series of 
papular areas between the carinal and 
superomaeginal plates, the latter never 
conspicuously enlarged nor overlap- 
ping the carinals. Genotype, Zoro- 
aster sacculatus, Fisher,, .......... 
ce*, No adradial plates; one series of very 
small adradial papular pores ; supero- 
marginal plates of two sizes, alter- 
nately larger and smaller, overlapping 
the carinals strongly and dominating 
these plates, which are sunken below 
the level of the superomarginals, 
Genotype, Bythiolophus acanthinus, 
USHER gars oc ee ed Gree Rete Setter cieks 
a’, Abactinal plates of disk, the carinals, ad- 
radials (when present), marginals, and 
sometimes one series of actinolateral plates 
devoid of spines or any conspicuous arma- 
ture, 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. 
b'. With a series of adradial plates more or 
less well developed; four or five series of 
actinolateral plates. Genotype, Cnemi- 
aster wyvellet,, Sad OW ose 6 yeles cass - 
b?, Adradial plates absent, the inner lobe of 
the superomarginal plates overlapping 
the carinal plates; three series of actino- 
lateral plates with rudimentary fourth 
series in large specimens. Genotype, 
Zoroaster sigsbeet, Perrier ......+.. abe 
389 
Myzxoderma *, Fisher 
Bythiolophus*, Fisher, 
Cnemidaster {, Sladen. 
Mammaster, Perrier, 
Key to the North Pacific Species and Subspecies of Zoroaster, 
a’. With four series of actinolateral plates on 
proximal part of ray; dorsolateral and 
intermarginal papular areas very small 
with normally one papula each; infero- 
marginal and actinolateral spines slender, 
closely apressed. 
* Myzxoderma, Fisher (subgenus), Bull. Bureau Fisheries, 1904, 
vol, xxiv., June 10, 1905, p. 316. 
+ Bythiolophus, Fisher, ‘ New East Indian Starfishes,’ Proc. Biol. Soc. 
Washington, vol. xxix., Feb. 24, 1916, p. 31. 
¢ I have examined large adult specimens. 
of the adult. 
Sladen’s type was small, 
very immature, and therefore had not developed some of the characters 
Ann. & Mag. N. Hist. Ser. 9. Vol. iii. 2 
6 
