ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 49 



about one-half form a poriphoral series ami are a trifle slenderer and lonj^er. On 

 the smaller paxilla^ the spinelets decrease markedly in size, but only sli<jhtly in 

 number. 



Abactinal plates in a prepared specimen, from inner or coclomic side. Plates 

 small, closer together along midradial line and in center of disk where there are no 

 papulae than at sides of area where papulae are present. Plates of latter region are 

 circular in general shape, but nearly always more or less irregular; with four, five, or 

 six short, abrupt, lobes irregvdar m length, thickness and m distribution on the periph- 

 ery of plate. These plates of papular area are arranged m ])erceptible, although 

 irregular, oblique transverse rows (parallel with interradial line). Usually six 

 papulte occur around each plate (often five, and rarely four) emerging between the 

 irregular lobes by which plates usuallj' touch. Plates along median area of ray are 

 even less regular than others, and frequently there are no lobes at aU. They are 

 slighth' smaller, and papulae are absent from a strip about four plates wide. Toward 

 center of disk, plates decrease rapidly in size, become more crowded, and lobes if 

 present are very mconspicuous and of irregular occurrence. The large primarv' 

 interradial plate placed just adcentrally to the madreporic canal is convex internally 

 (bears a large paxilla externally), and is slightly concave on the outer edge, next to 

 madreporic canal; three or four other less regular and smaller plates complete the 

 circle about the madreporic canal. 



Superomarginal plates, fifteen in number from median interradial line to 

 extremity of ray form an arched bevel to border of abactmal surface; plates shorter 

 than wide, but increase in length on outer half of ray. Plates of both series separ- 

 ated b}' transverse narrow deep fasciolar grooves and a narrow deep groove from 

 inferomarginal series. Superomarginal plates covered with short, terete, blunt, 

 granuhform spinelets, similar to but larger than paxillar spinelets, becoming well 

 defined, slender spmelets in the fasciolar grooves. The superomarginal spinelets 

 are close-set and small, forming an even nap on the exposed surface of plates. 



Inferomarginal plates much wider than long, encroaching more onto actinal 

 area than do superomargmals onto abactinal, and correspondmg in position to 

 superomargmals. Spinelets, densely covermg surface of plates, larger than those of 

 superomargiuals, and increasing in size toward outer end of plate which projects 

 slightly beyond adjacent end of superomargmal, thus definmg the ambitus. Infero- 

 marginal spinelets somewhat granuliform in middle of plate, often attaining a 

 squamiform appearance near outer end; spinelets in fasciolar furrows, slender. 

 Spinelets on extreme upper or outer edge of plate (above the squamiform spinelets) 

 are similar to those of adjacent portion of superomargiuals, the true ambitus or 

 edge of ray being a little below the margm of plate. It is on this rounded edge of 

 ray that the largest spinelets occur. Xo enlarged spines or tubercles on either 

 marginal series. Terminal plate small, granulose, deeph' notched below. 



Actinal interradial areas large; mtermediate plates low-paxilliform, arranged 

 in chevrons, the series adjacent to adambulacrals extcnduig about three-fourths 

 length of ray or to eighth inferomarginal. Plates decrease in size toward margin, 

 are strongly imbricated intemallj-, and the paxillar crowTis which are composed of 

 about twenty-five to thirty clavate obtuse, not very crowded, spinelets (slender 

 57444°— Bull. 76—11 4 



