98 ZOROASTERIDAE. 



figures of zea and wyvilUi published by Alcock, Sladen, and Fisher. But as I 

 have not seen a specimen of either of these last two forms, which Fisher intimates 

 may be identical, I consider the number of vahd species in Cnemidaster still 

 uncertain. I think nudus is undoubtedly distinct from the East Indian forms 

 but the three latter are certainly very closely aUied. 



Key to the species of Cnemidaster. 



Spinelets of actinal surface with thin sacculation scarcely noticeable when dry, not covering the plates 

 very closely. 



Distal carinals, and often marginals, with a central spine about as long as plate wyvillii. 



Distal carinals and marginals unarmed, but often with one or more minute spinelets or elongated 



granules nvdus. 



Spinelets of actinal surface flat, more or less squamiform, with heavy sacculation, closely covering the 

 plates. 

 Intermarginal papulae present; adambulacral ridge (on each alternate plate) with three stout spine- ' 



lets squamens. 



Intermarginal papulae wanting; adambulacral ridge "bearing a row of three sabre-shaped spines 

 and deep witliin the furrow a slender spinelet " zea. 



Prognaster. 



Perrier, 1891. Mem. Soc. Zool. France, 4, p. 259. 

 Type-spedes: P. grimaldii Perrier, 1891. Loc. cit. 



Perrier, in his later, fuller account (1896. HirondeUe Stell., p. 22), says 

 very emphatically that so far as he could see the adambulacral plates all extend 

 equally into the frn-row. This is so unusual a character for an adult zoroasterid 

 that one can but suspect that Perrier has faUed to examine the adambulacral 

 margin with sufficient care. If he is correct, the genus is easily recognizable. 

 The only known species was taken by the Prince of Monaco, near the Azores, 

 in 1,568 fms. 



Pholidaster. 



Sladen, 1889. Challenger Ast., p. 426. 

 Type-species: P. sgiiamatus Sladen, 1889. Lee cit. 



Although Sladen pubhshed a short notice of this genus in 1885, he mentioned 

 no species and hence the name must date from 1889. He never designated a 

 type but Fisher (1919. BuU. 100 U. S. N. M., p. 484) has done so. The two 

 known species were taken in the East Indian region : — squamatus in the Phihp- 

 pines in 100 fms. and distinctus in the Banda Sea in 140 fms. The Albatross 

 took squamatus at five stations in the Pliilippines in 108-218 fms. These are 

 all remarkably sUght depths for a member of this family. 



