96 ZOROASTERIDAE. 
While Mammaster remains monotypic, the following species are to be referred 
to Cnemidaster: — wyvillei, squameus, zea, nudus. 
At the same time that he proposed Mammaster, Perrier also seems to pro- 
pose a new genus, Prognaster, with Z. longicauda as the type. He had however, 
three years earlier (1891. Mem. Soc. Zool. France, 4, p. 259) given the same 
name and diagnosis to a genus with a new species, grimaldi, as the type. This 
earlier publication of the name is only referred to casually and ambiguously in 
the later paper, the user of the Travailleur and Talisman Report being thus 
completely and quite needlessly misled. The discovery of the many long- 
armed Zoroasters of the Indian Ocean has made the proposed genus as repre- 
sented by longicaudus quite untenable and I am not able to find any satisfactory 
basis for separating that species from the more typical species of Zoroaster. 
But if Perrier is correct in his statement regarding grimaldi that the adambula- 
cral plates are all alike, the genus Prognaster may well be retained for so unique 
a zoroasterid. 
In 1905, Fisher (Bull. U. 8. Bur. Fish., 24, p. 316) proposed a subgenus 
Myxoderma for two new Zoroasters, sacculatus and evermanni, designating 
sacculatus as the type. This group, to which platyacanthus H. L. Clark also 
belongs, is well-characterized and Fisher has recently (1919. Ann. Mag. Nat. 
Hist., ser. 9, 3, p. 387) given it full generic rank. But evermanni proves to be 
a true Zoroaster. Another genus described by Fisher (1916. Proc. Biol. Soe. 
Washington, 29, p. 31) is Bythiolophus, based on material collected by the 
Aupatross in Buton Strait, Celebes. This seems to be quite distinct from 
anything hitherto known in the family. Finally mention must be made of 
Sladen’s (1889. Challenger Ast. p.426) genus Pholidaster, recently rediscovered 
by the ALBATROSS. 
There are then seven apparently valid genera of Zoroasteridae. 
Key to the genera of Zoroasteridae. 
A. Primary plates and usually additional disk-plates conspicuously large, convex (often swollen), 
and more or less bare. 
B. First carinal plate, just distal to primary radial, conspicuously enlarged, larger than the adjoin- 
ing second marginals which are very much larger than the first ones; adradials wanting; three 
series of actinolaterals with beginnings of a fourth in large specimens........ Mammaster. 
BB. First carinal scarcely or not at all larger than the first marginals which are evidently larger than 
the second; adradials present; four or five series of actinolateral plates...... Cnemidaster. 
AA. Disk-plates not conspicuously convex or swollen, or if so, closely covered with spinules. 
B Adambulacral'plates‘all alike: < 2o..5.02h..0. sesso ee once Prognaster. 
BB.‘ Every other adambulacral plate with a conspicuous ridge projecting into furrow and carrying 
long spines. 
