JO BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



and heavier than the succeeding ones, and bear a subcircular, flaring truncate clavi- 

 form tip. The tip appears as if sharply cut off with a knife and is provided with 

 numerous sharp points. The end of the spines narrow as the spine lengthens. The 

 fifth spine from base of ray is about as long as three consecutive plates and the tenth 

 about as long as four; succeeding spines reach a length of 4.5 to 5 plates in length. 

 The inner subambulacral is somewhat shorter, slenderer, and usually is only slightly 

 thickened at the tip on the proximal plates. But in the cotype on two of the rays 

 some of the proximal plates have the second or inner subambulacral spine nearly or 

 quite as large as the outer, and have only one aboral furrow spinule. (See pi. 1, 

 fig. 36.) On the distal plates there is but one (distal) furrow spinelet. Some plates 

 have a spinelet just adorad of the middle and directed into the furrow, or about mid- 

 way between the middle and the adoral margin of the plate. There does not seem to 

 be any regularity in the presence of this spinelet which is about the length of the 

 shorter of the two aboral furrow spinelets. The sheaths covering the adambulacral 

 spines are closely covered with minute pedicellariae. 



The joint between the first and second adambulacral plates is nonmuscular, 

 the transverse edges of the two plates being fitted tightly together. The ray breaks 

 off at this point. The first two adambulacrals of any ray are fused by their lateral 

 faces with the corresponding two of the adjacent ray by a nonmuscular joint. The 

 first two lateral or marginal plates are similarly joined. There is a continuous series 

 of marginal plates from the interbrachial angle to the first spiniferous marginal 

 (about 15 plates). The articulation surface of the second pair of ambulacral ossicles 

 (distal face) where a ray has been broken from disk is rather high and narrow and 

 broader above than below. (See pi. 1, fig. 1.) This articulation surface is one 

 side of a nonmuscular or syzygial joint. 



Mouth plates small, joined to first adambulacrals by a muscular joint; acti- 

 nostomial margin rather short. Armature: on the actinostomial margin three, 

 or two, spinelets; the outer slightly longer than the innermost; near the aboral 

 margin of each plate, a transverse series consisting of one or two furrow spinelets, 

 and a tapering, pointed, suboral spine as long as the first three adambulacral plates. 

 All the spines and spinelets bear pedicellariae. 



Madreporic body prominent, about its own diameter from the margin of disk. 



Gonads very numerous, serially arranged along the genital stolon. The ovaries 

 are spherical bodies, the largest about 3 mm. in diameter. Numerous smaller ovaries 

 are crowded among the larger, and they all decrease in size on the outer half of the 

 long genital region. The testes are also numerous, and each is a many-lobed body, 

 the series extending to the end of the genital region. The surface of the ambu- 

 lacral plates facing the coelom is roughened by many little points or thornlets, which 

 in the male seem to be, in some cases at least, ossifications between the crowded 

 lobes of the gonads where these press against the ambulacralia. 



Type.— Cat. No. E. 1413, U.S.N.M. 



Type-locality.— Station 3342, off British Columbia, 52° 39' 30" N., 132° 38' W., 

 1, 588 fathoms, gray ooze, coarse stones; bottom temperature, 35.3; four specimens. 



Distribution. — Known only from the type-locality. 



Remarks. — Craterobrisinga synaptoma is a very distinct species, so far as the pres- 

 ent knowledge of this group of forms allows one to judge. It is the only species 



