72 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



more meshes merge in a transverse way forming a very wide interval, extending 

 occasionally from the superomarginal to the adambulacral plates. Bounding the four 

 longiseries of meshes there are two series of slender, four-lobed marginal and three 

 of actinal plates. These plates are connected, in transverse series, by a slender 

 intermediate ossicle between the superomarginal and inferomarginal plates, between 

 the latter and the first actinals, and sometimes between the first and second actinals. 

 Intermediate ossicles appear sporadically in the longitudinal series, but not regularly 

 and they all tend to disappear on the outer part of ray. There is an irregular series 

 of slender-lobed, +-form carinals, and between these and the similar superomarginal 

 plates are two series of very large dorsolateral skeletal meshes, separated by an irregu- 

 lar series of largely three-lobed plates. (Owing to the condition of the type, it is not 

 possible to ascertain the constancy of this arrangement for all the rays.) These 

 dorsolateral plates are connected with the carinals and superomarginals by slender 

 intermediate ossicles. The primary plates and most of the intermediate ossicles 

 bear a very small spinelet (pi. 29, fig. 26) with three or four terminal points, 0.4 to 0.5 

 mm. long. These are a little more delicate and have fewer terminal points than those 

 of coscinactis. The skeleton differs from that of coscinactis in having larger meshes, 

 with slenderer lobes to the plates; two rather than three dorsolateral series of meshes; 

 proximally three series of actinal plates (and papular areas). 



The dorsolateral and intermarginal papular areas have three to five papulae; 

 the others, one or two. 



First 8 or 10 adambulacral plates carry a transverse comb of three, rarely four, 

 very slender spines, the other plates two, equal in length to about four consecutive 

 plates. They are similar to those of coscinactis but are slenderer. 



Each mouth plate carries five or six spines; one or two on the actinostomial 

 end ; a row of three or four in line with the larger actinostomial spine, reaches nearly 

 to the outer end of the plate; sometimes there is a small spine as in coscinactis, on 

 the margin and near middle of plate. The plates are not very different from 

 those of coscinactis. 



There are no straight pedicellariae. The crossed pedicellariae are more tapered 

 than those of coscinactis as viewed in profile, the exact difference being best appreciated 

 by comparison of figures. (PI. 29, fig. 2, 2a.) The largest ventral pedicellariae 

 measure 0.45 mm. long; the dorsal 0.27 to 0.32 mm. 



Madreporic body very small, circular. Furrow narrow; tube-feet strictly 

 biserial. 



Type.— No. 32477, U.S.N.M. 



Type-locality.— Station 5675, off San Pablo Point, Lower California (27° 07' 

 08" N., 114° 33' 10" W.); 284 fathoms, green mud, fine sand; bottom temperature, 

 44.6° F. (March 15, 1911). 



Distribution. — Known only from type-locality. 



Remarks.— The, type specimen, recorded by Clark (1913, p. 202) as PediceUaster 

 improvisus Ludwig, is larger than the type of coscinactis and has conspicuously larger 

 skeletal meshes. The superomarginals are much nearer to the carinals than to the 

 adambulacral plates. On the ray that is best preserved and most regular there 

 are large subquadrate meshes between the carinals and adambulacrals ; four of these 

 series are between the superomarginal and adambulacral plates. It is not possible, of 

 course, to ascertain how constant the differential characters will prove to be. 



