ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FJiJHEK. 149 



number and arrangement of pedicellarise is very irreo^ular. Intenaediate plates 

 extend to about the fourth inferomarginal and each has one to three unequal 

 stumpy spinules. 



Madrcporic body circular, situated remote from margin, so that outer edge is 

 about mitldle of minor radius, or even adeentral to the middle point. In B. spirwsus 

 the madrcporic body is nearer margin, so that its inner or adeentral edge is at the 

 middle of r, or outside of middle. 



Anatomical notes. — Superambulacral plates absent, but their place is taken 

 by a thin dorsal carina of the ambulacral ossicles. The outer end of tliis is fastened 

 to the supcromarginal plate, while the main axis of the ossicle abuts against the 

 inferomarginal. Gonad confined to disk, opening close to margin and interradial 

 hne; interradial septum membranous. Intestinal ccecum ^\^th four obtuse divi- 

 sions; no real distinction between dorsal and ventral stomachs. Polian vesicle in 

 each interradius except that of madrcporic body. TSvo ampulhv: tube feet with 

 small sucking disks. 



Variations. — Individual variations have already been noted in the description. 

 The most important of these is the variable number of odd interradial marginal 

 plates. 



Young. — A young specimen, R=30 mm., r=5 mm., lacks pedicellariif anil 

 bears a striking resemblance to young B. spinosus except that there are only two 

 unpaired interradial superomarginals. The characteristic abactinal spines of the 

 disk are present and verj^ conspicuous, while the other abactinal plates bear a 

 single tiny spinelet each. A similar-sized indi^•illual of B. spinosus has onU' one 

 or two disk spines and very prominent unpaired interradials. 



Type.— Cut. No. 27803, U.S.N.M. 



Type-locality. — Albatross station 2859, off Prince of Wales Island, British 

 Columbia, 1,.569 fathoms, gray ooze; eight specimens. 



Distribution.— Knov,'n only from type-locality. 



Remarks. — As already intUcated, tliis species in general appearance most 

 nearly resembles B. spinosus Verrill, but differs in having an abundance of abactinal 

 and inferomarginal pedicellarijp, only one large inieromarginal spine vrith. a shorter 

 companion below it, shorter raj's, as well as a broader disk, and in lacking one or 

 more odd interradial superomarginals. From B. pedicifer (Sladen) it differs in 

 having much shorter rays, larger disk, less numerous furrow spinelets, one less 

 actinal adambulacral spine, more prominent abactinal disk spines, and also in respect 

 to the variable otld interradials. B. pedicifer was taken by the Challenger south 

 of the Cape of Good Hope and west of the Crozet Lslands. Sladen notes the same 

 variation in abactinal spinelets in pedicifer that occurs m mutabilis. From B. acan- 

 thonotus, mutabilis differs in respect to the abactinal spinulution, the former having 

 a delicate spinule on each plate of ray, not one or more very insignificant spinelets; 

 in the restriction in acanthonotus of the inferouiarginal pedicellariaj to the base of 

 ray. .Ul pedicellaria; in mutabilis have shorter and thicker often webbed spinelets, 

 and the actinal interrailial regions are larger and fuller. The ilifference in inter- 

 radial plates also holds, and the madrcporic body is nearer margin in acanthonotus. 

 From B. antarcticus Sladen, mutabilis differs in having only one superomarginal 



