176 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



but resembling ver_v large paxillse; furrows between plates usually conspicuous. 

 Abactinal paxillse with stellate imbricating plates arranged in longitudinal series 

 on rays, bearing low stout tabula crowned with numerous granuliform spinelets. 

 Papula one, two, or three to each area; six areas about a plate; absent from end 

 of rav. Adanibulacral plates with a dense armature of ten to twelve robust 

 subcylindrical spines or spinules, decreasing in size away from furrow; two or three 

 on furrow margin, and the rest in subparallel rows of two or three. Adanibulacral and 

 mouth spines arc the largest ones on animal. Mouth plates prominent with angular 

 marginal series situated on side of plate between true margin and peristome and 

 with numerous stout coarse spines on the actinal surface. Usually a single large 

 tooth at inner angle of combined plates, with several slightly smaller accessory 

 spines. Actinal interradial areas large, but narrow on rays; plates arranged in 

 interradial or transverse rows, densely covered with spinelets. Superambulacral 

 plates present. 



Description. — Abactinal surface varies in the degree of inflation, usually 

 arched on rays and disk. It is covered with fairly large and compact, rather 

 closely placed, tabulate, low paxillae, which are arranged in rather indefinite trans- 

 verse oblique rows at the sides on the proximal portion of rays, but are without 

 order on distal half and on central portion of disk. The paxillse also form not very 

 definite longitudinal rows on basal portion of rays, the mid-radial series being 

 largest and fairly definite as far as middle of ray. On either side of this the paxillse 

 decrease in size toward margin. These paxillse are not of the high slender sort 

 characteristic of the Astropectinidse, but are low, with broad flat tabula (like those 

 of Mediaster) crowned with robust clavate or acorn-shaped granuliform spine- 

 lets or elongate granules. These spinelets, which vary greatly in shape, from 

 roundish polygonal with a broad dome-shaped or neai'ly truncate tip to thimble- 

 shaped or even acutely ovoid, form a hexagonal, roundish, or cjuadrate very slightly 

 convex group of twenty-five to forty on large plates and fifteen to twenty-five on 

 the smaller lateral ones according to size of specimen (largest with R=140 mm.). 

 Those in center are usually shorter than granules about the edge, sometimes smaller, 

 sometimes slightly larger. The photographic figure will give the best idea. In 

 addition to the above, one or two irregular peripheral series of very much smaller, 

 an<l considerably slenderer papilliform, lanceolate spinelets are placed lower down 

 on the pedicel, and appressed closety to bases of outer robust spinelets, so that 

 they are not usually superficially visible. Superficially the papulae are easih* seen 

 between the paxillse, two or three to an area in the two largest individuals, usually 

 only one in a specimen with R = 74 mm.; six areas about each plate. 



Abactinal plates viewed from irmer or coelomic side are seen to be strongly 

 stellate, with usually six, but sometimes only five or four lobes. By these lobes 

 the plates overlap one another after the manner shown by the drawing. They 

 are arranged in regular longitudinal series parallel with the median radial. The 

 manner in which either adradial series overlaps (as seen from the imderside) the 

 radial series is shown by drawing. Notice that tliis is different from the overlapping 

 of the other parallel series. At the proximal end of the regular radial series is an 

 easily distinguishable primary radial plate. Between this and center of disk 

 the plates are smaller, less miiform in size, and irregular in disposition. On the ray 



