154 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



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

 diplacanthid, following which, after a few plates of three and two, the regular trip- 

 lacanthid plates commence. The spines are slender, about as long as the inner 

 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 Kam- 

 chatkan example is diplacanthid, and near the end of the ray, irregularly diplacan- 

 thid and monacanthid. 



Actinostome very small. Mouth plates with two apical spines in nearly verti- 

 cal 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 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 specimens they appear to 

 occupy all the space between the prominent circles of crossed pedicellariae surround- 

 ing the spines. The size of the areas increases with age; about eight or nine areas 

 can be counted across the 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. 



Straight pedicellariae (pi. 59, figs. 2, 2a-2f): There are two sorts, 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 inter- 

 marginal and actinal integument, and a few occur on the inferomarginal, actinal, 

 adambulacral, and oral spines. They vary to lanceolate obtuse and lanceolate acute. 

 In large specimens the abactinal measure about 0.9 to 1 mm., while the actinal inter- 

 radial 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. 



Small crossed pedicellariae (pi. 59, figs. 2g, 2h) are very abundant singly and in 

 groups among the papulae; in a broad zone around the abactinal and marginal 

 spines; and in half-wreaths on the outer side of the actinal and adambulacral spines. 

 The abactinal measure 0.27 to 0.3 mm. while the adambulacral measure 0.35 to 0.4 

 mm. (large specimens with R 270 mm. or more). Apparently there is a gradual 

 increase in the number of crossed pedicellariae, especially the papular, with age. 



Madreporic body large, subplane, with a row of spinelets on the adcentral border; 

 it is situated a little less than one-third r from center of disk. 



Variations. — The chief variations have been noted in the foregoing account. 



