150 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



thickly covered with crossed pedicellariae. On the outer part of the ray the vestigial 

 intermediate ossicles disappear entirely, while the marginals become very small. 



The inferomarginal plates which are also disconnected, except at the base of the 

 ray, each carry two equal somewhat flattened, blunt or truncate, stout spines (sub- 

 equal to the superoniarginal) involved in a single sheath, which generally exceeds the 

 spines in length, and has an expanded convex summit closely beset with crossed 

 pedicellariae. Vestigial intermediate ossicles subtend the ends of many of the proxi- 

 mal inferomarginal plates but disappear entirely on the outer half of the ray. (PL 73, 

 fig. la.) 



Adambulacral plates small, thin, the surface sunken somewhat below that of 

 the inferomarginal plates which overlap them. The single spine is slender, a trifle 

 tapered, blunt, or else un tapered and subtruncate, and devoid of pendant pedicellariae. 

 Small pedunculate lanceolate straight pedicellariae occur on the furrow face of the 

 plates. 



Papulae large, numerous, in ill-defined longitudinal bands abactinally, and 

 several to each intermarginal mesh. None actinal. 



Actinostome not at all sunken. Mouth plates prominent with usually two 

 chisel-shaped actinostomial spines shorter than length of plate and one similar, or 

 more tapered, suboral spine near the outer end of plate. The lateral or outer actino- 

 stomial spine bears a flap of tissue covered with numerous very small lanceolate straight 

 pedicellariae. The first pair of postoral adambulacral plates is enlarged and in con- 

 tact interradially; the second pair is widely separated. The median suture of the 

 first pair of plates is shorter than that of the oral plates. 



Ambulacra! furrows wide, with large, very crowded, quadriserial tube-feet. 

 The ampullae are single and very large. The furrow widens at the base, in a very 

 characteristic way, for the length of the first 8 to 12 ambulacral plates. The first 

 two combined ambulacral ossicles are conspicuously enlarged; the others are very 

 thin, and the pores are in four distinct series. The actinostome is large and apparently 

 very flexible. The nerve cord of each ray widens abruptly as it approaches the 

 actinostome and the circumoral cord, or fold, is conspicuous. 



The madreporic body, sometimes invisible, is situated near the edge of the disk 

 and surrounded by several spinelets. 



Small crossed pedicellariae (0.2 to 0.22 mm. long) are situated, as detailed above, 

 on the distal surface of the abactinal and marginal spine sheaths. Their form is 

 best appreciated by the figure. The enlarged tooth on one side of the jaw and the 

 numerous shank teeth are characteristic. 



Straight pedicellariae are small, slender to broadly lanceolate but delicate and 

 compressed; jaws apparently never spatulate. They are scattered over the surface 

 of the body and occur on the furrow margin and outer actinostomial oral spine. 

 Length, 0.15 to 0.65 mm. 



One of the characteristic features of this species is the fact that the rays are 

 slightly spaced on the circumference of the disk so that there is no sharp intcrbrachial 

 angle. Back of the mouth plates there is a vertical, broad, axillary channel having 

 several fine furrows leading from the abactinal to the actinal surface. This axillary 

 region is bounded by a distinct constriction, or furrow, which encircles each ray at its 

 base; and beneath the skin, a series of small (invisible) plates extends upwards from 

 the interradial marginal plates to the abactinal end of the channel, the last plate 

 being probably the primary interradial. (PL 73, fig. 16, i.) This column acts as a 



