72 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



from an irregularly recticulate spinulation of small capitate, unequal spinelets; 

 typically one or two supermarginal spines proximally, three to five short tubercles 

 distally; usually one inferomarginal, and one or two series of actinal spines; adam- 

 bulacral spines proximally two, distally one and two alternating; crossed pedicellariae 

 abundant; marginal and actinal straight pedicellariae frequently with broadened 

 toothed jaws. Differing from acervata in having larger conical dorsal spines with no, 

 or onlj a rery few, smaller accessory tubercles. R = upward of 6.25 r, and upward 



of 200 nun. 



Description. — The type form as described and figured by Verrill, and abundantly 

 represented in the collection at my disposal is about the most easily recognized asteriid 

 of Bering Sea and the adj acent parts of the Arctic Ocean. It exists in nature, however, 

 in various guises which depart from the characteristic form above alluded to, and 

 bridge pretty completely the gap separating the type subforma from that of acervata. 



The largest specimens, upward of 200 mm. major radius, are considerably bigger 

 than any acervata that I have examined. 



K 200 mm., r 32 mm., R = 6.25 r; breadth of the ray at widest part 40 mm., 

 at base 33 mm. Rays swollen at base, very gradually tapered to a blunt extremity; 

 rays and disk usually well arched and sometimes inflated. 



Abactinal surface beset with numerous, unequal, spaced capitate spinelets, 

 constricted above the base, then enlarged into a subglobose, acorn-shaped, or swollen, 

 subtruncate extremity, usually with weak longitudinal striations. These spinelets 

 are similar to those of acervata, and define rather irregular small sunken areas occu- 

 pied by papulae and pedicellariae. Arising from the general level are relatively few 

 much larger convex plates, bearing stout striated subcorneal or acorn-shaped blunt 

 or subacute tubercles, which in large specimens attain a length of 3 mm., or 5 mm., 

 including the convexity of the plate. These tubercles vary in number and position 

 but are more frequent along the radial line than on the dorsolateral regions. Occa- 

 sionally they form three irregular series, but with more spines in the radial than in 

 either lateral row. They stand singly or in groups of two to five (in which case one 

 is usually larger than the others) ; and in some specimens certain of the minor spines 

 may form intermediate tubercles by enlargement. The disk may entirely lack the 

 large spines (type variety) or may carry upward of 20; station 3251. The number 

 of large spines on the rays varies greatly, ranging in general from 5 to 30 to each ray. 

 A very large example from station 3440 (pi. 40, fig. 2) has relatively few, mostly on 

 the outer half of the ray, while a medium-sized specimen from station 3251 (R. 78 mm.) 

 has about the maximum number in three series. As soon as the large primary spines 

 are accompanied by smaller ones so as to form an acervate grouping, the dorsal 

 surface approaches in appearance exaggerated cases of the type variety of acervata. 

 (PI. 38, fig. 2.) In definitely intermediate examples which can not be assigned to 

 either poh/thrla or acervata the enlarged spines occur in groups as in acervata, but the 

 central spine greatly overtops the others and is conical in form. The supermar- 

 ginal spines may or may not stand singly on a plate. 



Crossed pedicellariae are very numerous on the abactinal surface, densely cover- 

 ing the slopes of the plates leading up to the base of the large spines and surrounding 

 the minor spines in from one to three circles. Much less numerous straight pedi- 

 cellariae are scattered over the abactinal surface usually on the edge of papular 



