354 BULLETIN 100, UNIIED STATES NATIONAL MUSEUM. 



example (No. 399, Cebu, Challenger) has been recorded by Sladen 

 (1889, p. 351). This, also, agrees very j)oorly with the Paris speci- 

 mens which may be regarded as typical, but as I was unable to make 

 notes from a direct comparison of specimens, any general observations 

 would be uncalled for. 



Unless Pentaceropis is extraordinarily variable there are prob- 

 ably at least 2 forms going by the name of ohtusata. 



Pentaceroysis euqyJiues Sluiter (1895, p. 56) is a small species (R. 

 26 mm.) with marginal and abactinal spines. It is possibly a young 

 specimen and not a Pentaceropsis. The present species is placed in 

 the genus Pentaceropsis on account of the presence of a conspicuous 

 intermarginal series of plates and the externally nonreticulate dorsal 

 skeleton. The first character is of doubtful value. Sladen (1889, 

 pp. 343 and 350) gives it primary importance, but intermarginal 

 plates of quite noticeable size are present in large examples of 

 Oreaster hawaiiensis and O. occidentalis (Fisher, 1906, p. 1073). I 

 find small intermarginal plates (4 to 6 in each interbrachium) in 

 even medium-sized examples of O. nodosus^ completely obscured by 

 the granulation; still larger ones are present in 0. alveolatus and 0. 

 ■mammiUatus^ but apparently not in 0. reticulatus. I have not been 

 able to examine other species, but I have no doubt that the character 

 is widespread in the genus. 



Probably the most importance difference between Oreaster and 

 Pentaceropsis is the structure of the abactinal skeleton, which exter- 

 nally is not reticulate, although internally the short connecting 

 ossicles between the longitudinal rows of primary plates constitute 

 the beginnings of such a structure. The superficial skeleton is com- 

 posed of very numerous small ossicles closel37^ packed between the 

 conspicuous primary plates, and among the former are numerous 

 papulae not set off into separate areas. The abactinal skeleton is 

 quite similar to that of Asterodiscus. although internally the skele- 

 ton of the latter is obviously reticulate, having rather long inter- 

 mediate ossicles arranged stellately between the primary plates, and 

 forming sunken triangular areas. 



Genus ASTERODISCUS Gray. 



Asterodiscus Gray, 3847fl, p. 176; 1847J), p. 75; 1866, p. 5. Type, .4. elegans 

 Gray. 



KEY TO THE KNOWN SPECIES OB' ASTERODISCUS. 



0.^ Abactinal tubercles conical, more or less acute to hemispherical, or truncate 

 hemispherical ; R=less than l.S r. 

 h} Only the primary abactinal tubercles with a basal circle of granules; no 

 small granules thickly scattered between the tubercles; inferomarginal 

 plates subequal to superomarginals, the surface with several large gran- 

 ules and a small tubercle ; superomarginals abactinal in position, covered 

 with coarse granules; marginal granules of actiual intermediate plates 

 very coarse ; four or five furrow spines elegans Gray. p. 355. 



