ASTEBOIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER. 69 



horseshoe around the canal, are two other smaller, slenderer plates, closely joined to 

 the large one. The side toward marginals is without a specialized raised ossicle. 



Superomarginal plates thirty-two to a ray, without enlarged spinelets or tuber- 

 cles. General surface covered with short spinelets, dehcate except along median 

 transverse Une where they are clavate to thimble-shaped, increasing in size toward 

 upper end of plate (same spinelets are markedly squamiform in californicus). 



Armature of inferomarginal plates very similar to that of californicus, there 

 being usually two or three marginal spines obhquely placed, and, in a line, three 

 more spaced, smaller, spines along aboral edge of plate. The auxihar}' lateral 

 spines situated just adorad to the regular lateral spines on each plate are longer 

 than the same spines of californicus. 



Adambulacral furrow spines three or four, similar to those of californicus. First 

 actinal series with two spines, the aboral being much the longer, tapering, slightly 

 flattened, bluntly pointed, longer and slenderer than the corresponding spine 

 of californicus. The adoral member is about as long as the furrow spine which 

 stands opposite. Outer or second actinal series usually consists of three slender 

 untapered spines somewhat shorter than furrow spines and standing in a fairly 

 regular row. Near base of furrow two or three very small spinelets sometimes 

 stand on outer end of plate. 



Actinal interradial areas very small, paved with six or eight paxiiliform plates 

 in large specimens. Each paxiJla bears a floriform group of about eight to twelve 

 slender spinelets, of unequal thickness (more or less), those in center being usually 

 the stoutest. Occasionally there is a single central sharp spine. In specimens 

 from off Lower Cahfornia, and to a less extent in those from off San Diego, the 

 spinelets are, on some of the plates, grouped or coordinated to form a sort of pedi- 

 cellarian apparatus. Even the spinelets on the actinal surface of the adambu- 

 lacral plates are frequently arranged in a similar manner. As a whole the inter- 

 radial areas may be said to be very inconspicuous. 



Mouth spines similar to those of californicus, but the marginal series stand 

 slightly spaced from the intermediate spines, so that iimer end of combined plates 

 is broader and the three series, superficial, intermediate, and marginal, are more 

 clearly evident. All spines are slenderer and a trifle longer than in californicus. 

 Marginal spines, about seven between tooth and inner end of first adambulacral 

 plate, and about six or seven more minute spinelets continue the series two-thirds 

 distance to outer end of plate. 



Madreporic body concealed by paxillie, situated as in californicus anil crossed 

 by sinuous striae; tiny, spiniform knobs on ridges of californicus apparently lacking. 



Superambulacral plates well developed. The upper edge of each ambulacral 

 ossicle is produced into a thin lamina or ridge between consecutive pairs of ampullae, 

 the free edge being sharp and provided with verj' slender, irregular teeth, five or 

 six in number. These give the appearance of a comb. The upper end of each 

 plate is produced into a knob, bearing several very slender spinelets; or the knob 

 may have a sharpened edge bearing teeth. Between the knobs of opposite plates 

 pass the transverse muscles of the ambulacral ridge. Very tiny spinelets are 

 discoverable between consecutive knobs and transverse muscles of the ambulacral 

 ridge. The presence of a comb of spinelets or teeth on the upper edge of the ambu- 



