ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER. 175 



Sublamily MIM:ASTI<;RINJ1<: Sladen, 1S89. 



Mimasterinse Sladen, Challenger Asteroidea, 1889, p. 331. — Perkier, 1894, p. 2.52. — Verrili, 

 1899, p. 200. 



Genus GEPHYREASTER Fisher. 



Gephyreaster Fisher, Ann. and Mag. Nat. Hint., per. 8, vol. 5, Feb., 1910, p. 171. Typp, ilimasler 

 swi/ti Fisher. 



Diagnosis. — Related to Mimasfcr Sladon. l)iit <liil'ers in liaviiifj stout tabulate 

 paxilljB with strongly stellate bases by which plates overlap; in character of actinul 

 intermediate plates which, instead of bearing small tufts of spines forming spaced 

 paxillje, are densely covered with spinelets; in the armature of the mouth plates, 

 which have a peculiar angular marginal series situated between peristome and 

 superficies of plate on the inner end; superambulacral jilatcs present. Marginal 

 plates, adambulacral plates, and their armature, similar to those of Mimaster, the 

 first without enlarged spinules. 



Bemarks. — This genus is erected for the species which I called Mimaster sunfd 

 in 1905. Since then I have received two additional specimens, and these have 

 convinced me that I was in error in placing the species in that genus. The char- 

 acter of the low tabulate paxillas resembles Pseudarchasfer, from which, however, 

 the new genus differs in the form of the adambulacral armature and marginal 

 plates, and to a less extent in the character of the actinal intermediate plates. 

 The large sucking disks of the tube feet also ally Gephyreastrr swifti to Mimaster 

 and Psftidarchastfr rather than to any genus near Plutonaster. It is probable that 

 Mimaster has superambulacral plates and that Sladen overlooked them, as is very 

 easy to do in forms where they are feebly developed. The median tooth pointed over 

 the actinostome recalls some species of PseudarcJiaster. My own opinion is that 

 the present genus is intermediate in many respects between Mimaster and Psextd- 

 archaster, and I would therefore associate the three genera more or less closely in 

 the system. The resemblance of true Mimaster to Leptychasfer is also great, but 

 the difference in the tube feet is a more important barrier than is commonly 

 supposed. In passing, it might be well to call attention to the discrepancy in 

 this character between M. tizardi and .1/. cognatus. The latter has conical tube 

 feet with a little button (as in Astropectinid,r) at the tip. M. cognatus is really 

 not a ^fimaster but in all jirobahility a Lepty chaster. The present genus is also 

 more remotely allied to the Odontastrridir. 



GEPHYREASTER SWIFTI iFlsher). 



PI. 30, figs. 1-4; pi. 57, figs. 2, 2(t-e: pi. 59, figs. 5, 5a. 

 Mimaster swifti Fisher, Hull. 15ur. Fisheries for 1904, vol. 24, 1905, p. 301. 



Diagnosis. — Rays five. R = 114 mm.; r = 43 mm.; R = 2:65 r. Breadth of 

 ray at base between first and second superomarginals 50 mm. A large specimen. 

 R=140 mm.; r = 58 mm.; R = 2.5 r. General form large, robust, flattened; rays 

 broad at base, tapering evenly or else slightly arcuately, to a blunt extremity; 

 interbrachial arcs wide, rounded; abactinal surface slightly inllatc<l, sunken in 

 actinal interradial areas. Marginal plates conspicuous, without sjiecialized spines, 



