662 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



seems to be lacking except on the basal portion of each spinelet. 

 Some of the spicules are forked near the base, the two branches being 

 unequal. The spinelets are longer than the height of tabulum, and 

 owing to their extreme tenuity are well preserved abactinally only in 

 the interradial sulcuses. Over most of the abactinal surface the distal 

 part of the spinelets is broken off. On the interradii where the spine- 

 lets are well preserved those of neighboring paxillsB touch across the 

 interspaces, and each group is distally slightly convex. There are 

 between seventy-five and one hundred spinelets to an average sized 

 paxilla, and the paxillse decrease in size toward the end of ray and 

 laterally toward the marginal plates. 



The papulae are distributed all over the abactinal surface, except 

 at the very tip of ray, and laterally as far as the superomarginal 

 plates. Each plate is surrounded by four papulae except on the mid- 

 radial area, where there are sometimes five papular areas around each 

 paxilla, and often there are two papulae to an area. 



On the actinal surface of the distal half of each ray are three series 

 of paxilliform plates, slightly lower and larger than the lateral paxillae 

 of abactinal surface, arranged parallel to the still larger squarish 

 adambulacrals. The outer two, which are the marginals, toward the 

 base of ray diverge from the inner (which is the first actinal inter- 

 mediate series and reaches very nearly to tip of ray) and at the inter- 

 radial line are nearly on the ambitus, being separated from the adam- 

 bulacrals by about four longitudinal series of actinal intermediate 

 plates. These marginal plates are very small, and the inferomarginal 

 series is slightly the more regular of the two. The plates of the two 

 series are subequal and a trifle larger than adjacent abactinals. The 

 plates are so small that it is not possible to ascertain if an odd inter- 

 radial plate is surely absent; from a study of the arrangement of 

 adjacent actinal intermediate plates, I think they are. In one or 

 two interradii, however, it is difficult to be sure, as the plates are 

 pushed out of position. 



As mentioned above, one series of actinal intermediate plates nearly 

 reaches tip of ray, the second row reaches about two-fifths length of 

 ray measured along side (or about one-half R), while the third and 

 fourth rows contain only a few plates and extend but a short distance; 

 a few plates of a fifth row are present in two interradii. It is the inter- 

 polation of these three extra rows of intermediate plates which causes 

 the marginals to be crowded toward the ambitus. Spinelets of actinal 

 intermediate plates are about 0.675 mm. in length and are perforated 

 to the tip, which commonly ends in two or three short, sharp, glassy 

 prongs. The intermediate plates have prominent convex tabula and 

 overlap plates of both their own and adjacent series. The free edge 

 of the plate is toward the furrow and interradial lines. 



