EASTERN TROPICAL PACIFIC ASTEROIDEA. 97 
C. Carinal plates of ray smooth and bare surrounded by series of skin-covered squamules. 
Pholidaster. 
CC. Carinal plates not surrounded by series of skin-covered squamules. 
D. A conspicuous buttress (a specialized superambulacral plate) connects first two ambulacral 
plates with body-wall; superambulacral plates present. 
E. Adradial plates present; superomarginals not overlapping carinals......... ./ Myxoderma. 
EE. Adradial plates wanting; superomarginals strongly overlapping and dominating the 
GALINAIS; «2.5.12 ce eee eC ers Moen ee ee Ae Ree Serie a ale ais ote Bythiolophus. 
DD. Superambulacral plates wanting, and hence no buttresses between ambulacral plates and 
Dod yewallll «., <5): <.cceautern seta Seen rete auctor enya ern afez Bier omegevevekove cer sycawe haa ake Smit tee Zoroaster. 
Mammaster. 
PERRIER, 1894. Travailleur et Talisman Stell., p. 125. 
Type-species: Zoroaster sigsbeet PERRIER, 1880. Comp. Rend. 91, p. 436. 
This genus is still monotypic, for the allied East Indian species all differ in 
the character of the marginal plates at the base of the arms. Aleock (1893. Ann. 
Mag. Nat. Hist., ser. 6, 11, p. 111) considers three of his eight Zoroasters con- 
generic with szgsbeei, but he failed to note this particular feature which seems 
of no little importance. Fisher makes no reference to it and hence it does not 
seem to have attracted his attention. His work has shown that Alcock’s three 
species are Cnemidasters but he is not sure that Mammaster can be maintained 
as distinct from that genus. Mammaster is evidently not common as I have 
found no published records of its occurrence other than those in the BLAKE 
Report — one station near St. Christopher in 208 fms. and one in the Gulf of 
Mexico is 321 fms.; seven specimens altogether. The largest of the BLAKE 
specimens had R about 75 mm. Perrier selected a much smaller specimen 
(R = 49 mm.) for his description and does not refer to the large one. 
CNEMIDASTER. 
SLapEN, 1889. Challenger Ast., p. 423. 
Type-species: C. wyvillii SuapEN, 1889. Loc cit. Monotypic when established. 
The collections made by the ALBaTrRoss in the Far East have enabled Fisher 
to revolutionize our knowledge of this genus, which was based on a single very 
immature specimen. Fisher had seven specimens at his disposal and has been 
able to make clear some of the growth-changes. These bring out the impor- 
tant fact that the Zoroasters described under the names nudus, sywameus, and zea 
are all congeneric with wyvillii. Indeed the four species are so closely related, 
it is exceedingly difficult to separate them properly. The following key is the 
result of studying cotypes of nudus and squameus, and the descriptions and 
