gQ BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



drical, convex-tipped pedicel whi;h bears a crown of eight to twelve (type) very 

 slender, tapering needle-like spinelets, considerably longer than the pedicel, and 

 usually' standing upright in a cylindrical coordinate group, highly characteristic. 

 PaxilfiB m center of disk have irregular or circular bases. Small paxillae are scat- 

 tered here and there on the radial areas with only three or four spinelets. In some 

 specimens the spinelets are thicker, due to the investing membrane. On the distal 

 portion of ray the tabulum or pedicel of paxillae becomes gradually much shorter, 

 and at tip of ray the paxillte are convex spine-bearing plates. There is some vari- 

 ation in the diameter of the pa.xilla; but all specimens agree in having the char- 

 acteristic arrangement in transverse spaced rows. On an average three transverse 

 series correspond to one superomarginal plate. The paxillse resemble, frequently, 

 pseudopeilicellarise from the fact that the spinelets all converge and meet at one 

 point, forming a conical group. 



The abactinal ])lates viewed from irmer surface of dorsal integument are very 

 regular on the areas of regular paxillse, where, as mentioned above, they are ellip- 

 tical in general form, with a suggestion of a lobe at either side in medium sized and 

 small individuals. In large examples the plates are very distinctly spaced all over 

 the doi-sal surface, but in medium-sized specimens they usually touch, at least in 

 center of disk and along radial areas. The regularity of the plates is broken on 

 these areas; along the latter the plates become shorter and broader, often irregular, 

 while on the disk they are subcircular. The difference in appearance of the abactinal 

 plates in large and medium-sized examples seems to be due to the fact that beyond 

 a certain stage the paxillse do not increase in numbers in proportion to the increase 

 in size of the individual. Thus, an example with R^96 mm. has a width of ray 

 at third superomarginal of 22 mm. and twenty-seven to twenty-nine paxillse in a 

 row across the ray. The type, with R^176 mm., and a breadth of ray at third 

 superomai^inal of 36 mm. has only thirty-two to thirty-six paxillse. As a result 

 the paxillae are much more wndely spaced in large specimens. The papulse are 

 very conspicuous, and are distributed everywhere except at very end of ray. The 

 regular arrangement in double tran.sverse rows is interiiipted along radial line and 

 at center of disk, but papuUe are present in these regions. In many specimens the 

 papulse are as large as the paxilla- in diameter. 



Superomarginal plates, thirty-nine in number from interradial line, very tumid, 

 and not usually encroaching very conspicuously onto abactinal area proximally 

 of the middle of ray. Beyond this point the plates encroach more and more onto 

 abactinal surface, until considerably more of the plate belongs to the upper surface 

 than to side. Plates are subquadrate, except in interbrachial arc, where they are 

 much higher than long; abactinal margin of plates slightly rounded. There are 

 no fasciolar channels, but only a vestige of them, the surface sloping gradually 

 from the sutures toward the middle of the plate which bears a robust tapering 

 spine (or occasionally two), much longer than the plate (7 or 8 mm.^i and directetl 

 obliquely upward and outward. These spines are longest at about middle third of 

 ray, thence decreasing very gradually in length toward tip of ray. Many of them 

 are very curiously bifid for half or two-thirds their length, as if composed of two 

 fused spines, and, therefore, possessing two closely appressed points. Abactinal 

 margin of plalc I)oars one or two robust, upright, tapering, pointed spinules or spines 



