142 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



26 spines, crowded near the disk, but further apart near the extremity of the ray. Between this 

 row ami the marginal row there are scattered a few more of the larger kind, sometimes in clusters 

 or short rows of three or four. On the disk they form a more or less distinct pentagon, within 

 which there is another circle and a spine of large size in the center. The spines of the smaller 

 kind, minute, slender, and truncated, are scattered between the large ones. (Stimpson; see pi. 

 60, fig. 4, type.) 



The large spines are striated at the summit, and in large specimens the smaller 

 sort are also pretty definitely grooved. The smaller spines sometimes form trans- 

 verse rows, but they do not define the papular areas, or complete the reticulation as 

 in ulreolata, and intermediates. Four small specimens from near Tacoma have the 

 larger spines abnormally magnified and the smaller all but absent, while one from 

 Orca, Prince William Sound, Alaska, with R 65 mm., has the larger spines distinctly 

 acervate. 



The superomarginal spines are slenderer than the larger abactinal, usually 

 tapered and blunt, and form a very regular series which curves up at the interradius 

 to the level of the inadreporite. While the spines are generally single, sometimes a 

 small spinelet accompanies the larger. In giant specimens the principal spine is 

 often subcapitate, truncate, and striate. 



The inferomarginal spines (usually two to a plate proximally) are a little longer 

 and slenderer, pointed, blunt, or subtruncate, varying individually. In giant speci- 

 mens there are usually two spines to a plate. The intermarginal channel is definite 

 and well defined. 



Actinal plates in four series in very large specimens; in three series, in medium- 

 sized; and in two series in small specimens (R 20 mm.). In giant specimens they 

 generally carry two spines in an oblique row, except for the plates of the short inner 

 series which are monacanthid. In medium-sized examples there is usually one spine 

 to a plate; or three rows of actinal spines at the base of ray, then two, and finally one 

 on the outer half or third of the ray. But in giant specimens, where the plates are 

 diplacanthid there may be seven rows of actinal spines at the very base of the ray, 

 although the duplicate series of each range of plates is evident enough by rather 

 wide channels between the longitudinal rows of plates. The submarginal channel 

 is nearly as broad as the intermarginal channel. The spines are similar to the infero- 

 marginals and are variously cylindrical, tapered, or swollen, with blunt-terete or 

 blunt-compressed, or obliquely dressed extremities; or the whole spine is a trifle 

 curved upward. In very large examples the spines are shallowly grooved at the 

 tips. The spines are slenderer and longer than the larger abactinal spines, but in 

 medium-sized examples may be subequal in caliber. 



The adambulacral armature is alternately one and two spines to a plate, with 

 one on the first five or six (adoral) plates, and two on a variable number (usually 

 relatively few) of succeeding proximal plates. The spines are slender, tapered, blunt, 

 the furrow spine, as is usually the case, being the slenderer. Near the mouth the 

 spines become longer and slenderer forming a dense chevaux-de-frise over the acti- 

 nostome. In a giant example, R 270 mm., the adoral adambulacral spines are 8 mm. 

 long (or subtend the arc of the first eight adambulacral plates). At one-fourth R, 

 measured from the mouth, the spines are 5 or 5.5 mm. long. Medium-sized speci- 

 mens have two, giant specimens three (or four) adoral pairs of plates in contact 

 interradially. 



