78 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



r = 2.5 mm., R = 2.6r. The type-specimen, which is the largest knowii 

 example, measures: R = 21 mm., r = 6 mm., R = 3.5r. Width of ray 

 at base in various mature examples 5 mm. to 7 mm. 



Rays more or less long, slender, abactinally slightly convex, with 

 marked longitudinal ridges, actinally flat or concave. Disk of medium 

 size, abactinally convex and without interbrachial arcs. 



Abactinal area of rays occupied by a central range of radial plates, 

 on each side of which there is a range of accessory ossicles which 

 however do not attain the distal portion of the rays. In mature 

 rays there are in the proximal region also inserted a few plates on 

 each side of the intercalary columns. Outside of the latter are 

 the ranges of well-defined supramarginal plates which slightly overlap 

 the inframarginals. The marginal and radial plates are most promi- 

 nent, and all are highly carinate or pointed. There is a single large 

 spine on the apex of all radial and accessory plates and several 

 smaller ones are also arranged around it. The supramarginal plates 

 have numerous granules which bore articulating spines. The plates 

 of the disk can not be clearly made out, but in a small specimen 

 somewhat distorted there appears to be a small central plate sur- 

 rounded by a first ring of 7 ossicles followed by a second ring of 

 14 plates. These pieces are all nearly of a size. The medial ray 

 columns terminate in 5 large basal radial plates, while inside of 

 the proximal inframarginals there is no large interradial plate as in 

 Hudsonaster incomptus. 



Ambital area very illy defined, but in the angles between the large 

 infra- and supramarginal plates there are here and there inserted 

 tiny accessory pieces. In a young individual there are none of these 

 accessory plates. 



Madreporite unknown. 



Inframarginal plates distinctly granulated, completely inclosing 

 all other abactinal plates and common to both the abactinal and 

 actinal areas. In mature specimens there are from 15 to 20 plates 

 on each side of a ray. Laterally each plate has a Well-marked small 

 pit, probably the place of attachment for rather strong spines, none 

 of which however have been observed. 



Interbrachial areas with single, hexagonal, axillary interbrachial 

 plates. 



Adambulacral plates slightly elongate-subquadrangular, of which 

 there are from 18 to 20 on each side of a ray; distally they appear to 

 pass over and to cover completely on the actinal side the inframar- 

 ginal plates. Between the adambulacral columns there is a more or 

 less wide ambulacral furrow. Each adambulacral plate bears on its 

 inner edge a rather thick but short, slightly striate spine and several 

 minute ones. Or ad to each axillary interbrachial there is a pair of 

 prominent elongate-triangular adambulacral plates bearing spines, 



