4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 69 



are triplacanthid then irregularly diplacanthid and triplacanthid, 

 and finally on the distal third of the ray mostly diplacanthid. The 

 distribution of these numbers will, of course, vary in different indi- 

 viduals. In general the proportion of plates occupied by three 

 spines increases with the size of the animal, the third spine being 

 added on the outer side of the plate. The combs of alternate plates 

 are advanced further into the furrow. The first three plates follow- 

 ing the mouth plates are generally monacanthid; then three or four 

 are diplacanthid, following which, after a few plates of three and two, 

 the regular triplacanthid plates commence. The spines are slender, 

 about as long as the innter actinals. The furrow members are 

 slightly tapered; the others, a little stouter, varying from slightly 

 tapered to cylindrical, or somewhat clavate, round tipped to bluntly 

 pointed. The third, outer spine may be shorter than the other two. 

 There are usually five pairs of united plates composing the adoral 

 carina. The large Kamchatkan example is diplacanthid, and near 

 the end of the ray, irregularly diplacanthid and monacanthid. 



Actinostome very small. Mouth plates with two apical spines 

 in nearly vertical series, the smaller at the mouth of the furrow, the 

 other (about as long as the plate, and sometimes spatulate) almost 

 directly above it (as viewed from the actinal side). The suboral 

 spine, near outer end of plate, is about as long as first two or three 

 adambulacrals. 



The papulae have the distribution characteristic of the genus and 

 are very abundant, especially abactinally, where, in alcoholic speci- 

 mens, they appear to occupy all the space between the prominent 

 circles of crossed pedicellariae surrounding the spines. The size 

 of the areas increases with age; about eight or nine areas can be 

 counted across ray at base, but the dorsolaterals are very irregular. 

 There is a fairly regular supramarginal row. The intermarginal 

 and actinal rows — eight in all — are typically regular and decrease 

 in size toward the furrow. 



There are two sorts of straight pedicellariae, larger and smaller; 

 the larger, usually compressed ovate, wedge shaped, with the end 

 broadly rounded and the tip of each jaw with two or three denticles, 

 varies from abundant to relatively few on the abactinal surface; they 

 are generally abundant on the intermarginal and actinal integument, 

 and a few occur on the inferomarginal, actinal, adambidacral, and 

 oral spines. Thej^ vary to lanceolate obtuse and lanceolate acute. In 

 large specimens the abactinal measure about 0.9 to 1 mm., while the 

 actinal interradial ones are 1.5 mm. long. Much smaller ones are 

 present in variable numbers on the actinal, adambulacral, and oral 

 spines, and are rather sparsely scattered along the furrow face of 

 the adambulacral plates. 



