ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER. 185 



Sladen placed parelii in Tethyaster, a subgenus of Plutonaster, wliilo Bell, 

 Norman, Grieg, and Ludwig relegated it to Plutonaster. Such a course is untenable, 

 because Plutonaster belongs to a difTerent family altogether, and has pointed tube 

 feet, never sucking disks. This character alone is enough to exclude parelii from 

 Plutonaster. As a matter of fact, parelii is so near the type of Pseudar chaster [that 

 is, discus] that one is obhged to search carefully to find trenchant differences. The 

 following are the considerations which lead one to rank parelii in Pseudarchaster: 

 tube feet \\-ith sucking disks; character of the marginal plates, especially the infero- 

 marginals; the characteristic adambulacral plates and armature, which is totally 

 unhke Plutonaster; the actinal intermediate plates with spaced granules and 

 incipient central spinule; the armature of the mouth plates, there being an unpaired 

 median tooth directed over the actinostome; the presence of postadambulacral 

 fascicles very characteristic of Pseudarcliaster and never found in Plutonaster or 

 aUied genera. 



In a specimen of parelii from the Copenliagen Museum: R = 43 mm., r=14 

 mm.; superomarginals twenty-three; the superomarginals are considerably arched 

 above the abactinal paxillar area on arms; the latter is narrower than the mar- 

 ginal plates, there being at the middle of viiy only three longitudinal rows of paxilla-, 

 and only a single row reaches terminal plate; about four and one-half to four 

 paxilla; correspond to two superomarginals; furrow spinelets five or six; one or 

 two actinal spinelets enlarged sUghtly; first row of actinal intermediate plates has 

 incipient fascioles; a few of the actinal intermediate plates with sHghtly enlarged 

 spinelets. 



This specimen differs from the Alaskan cliiefly in having tumid superomarginals 

 and a narrower paxillar area on rays. There are about five transverse rows of 

 of granules on the superomarginals (the same as in Alaskan specimens). 



PSEUDARCHASTER PARELH ALASCENSIS Fishei. 



PI. 31, figs. 3-5; pi. 33, fig. 4; pi. 40, fig. 3; pi. 57, fig. 6. 



Pseudarchaster alascensis Fisher, Bull. Bur. Fisheries for 1904, vol. 24, June 10, 1905, p. 303. 



Diagnosis. — Very close to Ps. parelii, and dilTering in having shorter and 

 narrower superomarginals with less compact granules, less compact paxillar area, 

 papilhform inferomarginal s|)inclcts, more dehcate and longer actinal intermediate, 

 adambulacral, and moutii spinelets. The general facies of the two forms is different 

 enough, but the actual differences, allowing for individual variation, are not great. 

 R = 99 mm.; r = 34 mm. K=2.9 r. Breadth of ray at base 40 mm.; at middle 

 15 mm. 



Description. — Paxilla; are not markedly different from those of parelii, but are 

 slightly spaced instead of crowded, and a trifle smaller, the central sinnelets having 

 convex instead of flat tips. The figures will give the best idea of this difference. 



The superomarginal plates are decidedly narrower than in Japanese and most 

 northern specimens of parelii. In these the widest plates in interbracliial arc are 

 9.5 mm. (11 = 77 to 100 mm.) and in alascensis the same plates are 5.5 to 6 mm. 

 (R = 73 to 99 mm.). In alascensis the granules are not dose-set, forming a hard, 

 smooth mail, but are spaced and those on outer edge of plate are enlarged, with 

 strongly convex or conical subtubular tips. A specimen from station 4201 has 

 these enlarged into small subcoiiical spinules in the interbrachial arc. 



