fisher: the genus blakiaster perrier. . 163 



sparingly on the actinal intermediate and adambulacral plates. The 

 spinelets forming this apparatus surround a slight pit or depression 

 in the plate (Plate 2, fig. 5) and are similar though a trifle blunter 

 and stouter than the others, especially on the adambulacral plates. 

 Verrill figures two, and he found similar hut smaller ones with three or 

 tour blades on the marginal and abactinal plates. These pedicel- 

 lariae appear to be very similar to those occurring in some species of 

 Persephonaster, for example cingulatus from the Hawaiian Islands. 



There are well-developed superambulacral plates (absent from the 

 first ambulacral plate). The tube feet are pointed as in other genera 

 of the Astropectinidae, and the ampullae are strongly double. There 

 are no deposits in the tube feet. I have been unable to find an in- 

 testinal coecum. Verrill has found an anal pore in his specimen 

 but I can not be sure that the pore, which is present in the specimen 

 studied is not artificial. It is unusually far from the center of the 

 disk. The madreporite is small, near the margin, and the irregular 

 and relatively few, coarse ridges cross the body from one side to the 

 other in an interradial direction. 



Blakiaster shows closer resemblance to Persephonaster than to any 

 other genus of the Astropectinidae. In certain features it also recalls 

 Leptychaster. Its similarity to Persephonaster concerns the follow- 

 ing features which are essentially alike in the two genera. The tumid 

 marginal plates with their obsolete fascioles; the type of armature 

 of the inferomarginal plates; the madreporic body; the armature 

 and form of the intermediate plates. The adambulacral and oral 

 plates are very similar, the armature being much alike. In typical 

 species of Persephonaster the adambulacral plates are longer and the 

 margin is less angular and more rounded, with more numerous furrow 

 spinelets. In P. patagiatus (Sladen) the adambulacrals are rather 

 more angular than in P. cingulatus (Fisher) and in several unde- 

 scribed Philippine species, and the adoral facet is the shorter, but the 

 furrow spinelets are more numerous and the plates longer in propor- 

 tion to width than in Blakiaster. The number of spinelets is hardly 

 of generic importance. In Persephonaster as in Blakiaster there is 

 a moderate number of undifferentiated subambulacral spinelets; 

 none are specialized or enlarged as in Thrissacanthias and Sideriaster. 

 The compression of the first adambulacral plate varies in Persephon- 

 aster. It is less compressed than in Leptychaster, and in some species 

 more than in Blakiaster; in at least one species it is identical with 

 that of Blakiaster. The mouth plates of the typical species of Per- 

 sephonaster, and of Tritonaster have a peculiarity in the marginal 



