SS BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



following; are usually monacanthid. In the very large type most of the plates are 

 diplacanthid. The furrow spine of diplacantbid plates is shorter, slenderer, and 

 more obviously tapered than the others which are terete, slightly tapered near the 

 blunt tip, sometimes slightly compressed. In nicely killed specimens the spines 

 appear to form three longiseries al margin of furrow since the slenderer furrow spine 

 of diplacanthid plates is advanced into the furrow; its companion spine forms the 

 outer series, the middle being composed of the single spines of alternate monacanthid 

 plates. Adoral carina composed of three or four contiguous postoral adambulacrals, 

 the single spines of which are appreciably longer than those following. 



Mouth plates with n conspicuous apical, tapered, blunt or subacute spine (with 

 a snuill lateral companion) longer than the median suture, and a long slender tapered 

 suboral spine almost identical with the first few adambulacral spines, though a 

 trifle longer. 



Crossed pedicellariae (pi. 29, figs. 1, la-le) are very numerous, 0.29 to 0.31 mm. 

 long, in conspicuous wreaths (one to four tiers of pedicellariae broad) surrounding 

 abactinal and superomarginal spines, and scattered singly or in groups of two or 

 three among the papulae (type); in fairly large clusters on the outer side of infero- 

 marginal and actinal spines (along with straight pedicellariae in largest examples); 

 mixed with compressed broadly lanceolate straight ones, in clusters, on the outer 

 side of adambulacral spines. The last differ in form from the abactinal, being slightly 

 smaller (0.27 mm.) with a larger terminal portion to jaw, as seen in profile. (PI. 29, 

 figs, la, Id.) 



Straight pedicellariae numerous, large. (PI. 29, figs. 4, 4a-4/.) The abactinal 

 vary greatly in size and form, some having broad squarish dentate jaws, others 

 narrower dentate jaws with two or three teeth; still others are small, compressed, 

 ovate, edentate, as in coei. The intermarginal and axillary channels are conspicuously 

 provided with broad-valved toothed pedicellariae (upward of 1.25 mm. broad and 

 1.5 mm. high), veritable giants compared with the same armature of coei. Similar 

 but somewhat smaller ones are found among the actinal spines, where also there are 

 still smaller, compressed, ovate or broad-lanceolate pedicellariae without obvious 

 teeth, together with intermediate stages between the two. Some of the latter migrate 

 upon the inferomarginal and actinal spines in the largest example (Captains Bay). 

 The largest pedicellariae are much broader than the spines in small and medium-sized 

 examples and vary somewhat in number, but are always numerous. Ovate corn- 

 ed pedieellariae occur abundantly on the adambulacral and oral spines, and very 

 small ones singly or in clusters on the furrow face of the plates. The difference in 

 size between these and the intermarginals is enormous. 



Madreporic body conspicuous with fairly coarse striae, situated at nearly mid r. 



Tube feet fairly large, crowded in four series. Actinostome small, rather sunken. 



Young.— A specimen with R 28 mm., was taken with adults at station 4777, 

 and resembles the larger examples, but has only a few actinal spines at base of ray. 

 The characteristic large pedicellariae are well developed. The next size with R 67 

 mm. is adult, in respect to spines and pedicellariae. 



Anatomical notes.— The gonads (not mature in any example examined except 

 the large one from Captains Bay) are attached to the interbrachial septum on a level 

 with the inferomarginal plates, just a few millimeters adcentral to the interbrachial 



