382 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



pacli plato arc four or five slender, tapering, pointed, marginal spines, the inner 

 much the thickest and longest (about equaling interradial diameter of plate), and 

 a short distance back of this is a similar slender subequal suboral spine. The inner 

 marginal and suboral may have a sacculus; these are well developed in the largest 

 Alaskan example, which also has them on the aperture papillae and adambulacral 

 spinelets. 



Actinolateral membrane tliin, the spines showing through, over thirty in 

 mature specimens, the seventh to eleventh the largest. 



Color in alcohol rose pink; in hfe a deeper rose, madder, or scarlet. 



Anatomical notes. — Nidamental cavity spacious. Pedicels of paxillse slender, 

 shorter than spines, about as 1.75:3 along midradial region, and as 3:5.5 on lateral- 

 most row; base of paxillse ^\^th four long slender processes, imbricating \nth similar 

 processes of four other paxilliie. in such a way that very regular rhombic meshes 

 are formed, except between the two lateral ( = marginal) rows of paxilla; (which 

 do not alternate as do the abactinal, but stand one above the other). Counting 

 directly across ray from one superomarginal to another there are three rhombic 

 meshes, or two complete ones and two halves; likewise omitting' the two non- 

 altemating rows of paxillae of either side, there are five longitudinal rows of true 

 abactinal paxillae. Papulae large, ^^^th many small divisions at the summit; there 

 is one to each paxilla except the primary radial, and none occur within the circle 

 formed of the primary radial (or oscular) paxilla?. The periproct membrane 

 contains several rows of thin, spaced, roundish plates, wliich consist of a single 

 layer of characteristic calcareous mesh. No calcareous deposits are discoverable 

 in the abactinal integument (other than the paxillae) and none occur in the supra- 

 dorsal membrane. (Type, and specimen from station 3603 examined.) 



Anal aperture a narrow slit; intestinal caecum small, little more than a dila- 

 tion of the intestine. Gonad (female) interradial; interradial septa with thin 

 plates. Ampullae large, proximally single, but farther along the ray with two 

 parts (though essentially only two-lobed sacs). Tube feet in two rows, ^^^th a 

 small sucking disk, except near end of ray where the feet have an attenuate pointed 

 tip. First ambulacral ossicle enlarged and \\'ith the lateral wings of the large 

 odontophore forming a strong mouth frame; several large muscles to the stomach 

 are inserted on it. 



Young. — The type is an immature specimen. The cruciform abactinal plates 

 overlap slightly by the lobes, which are not fully developed. 



A series of nine specimens from station 2859 are graduated in size from R = 

 10 mm. to R = 42 mm. and exlubit well the changes which take place from the 

 young to the mature form. It is this instructive series which has led me to place 

 the San Diego and Alaskan specimens in the same species, although adults of the 

 latter appear at first sight to be considerably different in the possession of manj' 

 more spiracula, as well as lappets or saccuh to the segmental papillte. A specimen 

 with R = 15 mm. has the characteristic nine rows of alternating paxillae (each 

 with four spinelets) along the ray. The spiracula are much fewer than in the 

 adult, are scattered between the paxillar crowns, and are apparently a trifle more 

 numerous than in the type (although on account of the wliiteness of the membrane 

 it is difficult to see them in the latter). Adambulacral spines four, the aperture 



