92 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



Abactiiirtl plates or bases of paxillac small, and nearly the same size as in D. 

 eiimius, those of lateral regular series if anything a trifle larger and more regular. 

 These conmionly have five or six very short lobes, which become absolete at tip and 

 towartl margin "of area where the plate changes from a circular to an elongate con- 

 tour. The plates of the median radial region are rather more regularly arranged 

 than in enmius and are closer together. The carinal or midradial plates are 

 circular with very slight lobes on some of them, and adjacent plates touch them so 

 that the papular "areas are small, with single papulae. (In eximius the carinal plates 

 are spaced and strongly lobed with larger papular areas than ordinaiy.) On 

 the disk, especially toward the center, the plates are much smaller than in eximius. 

 They decrease rapidly in size toward the center where they are scarcely larger than 

 the diameter of pedicel or paxilla shaft, circular in outline and widely spaced. 

 Along the couise of either largo abactinal adradial muscle band the plates form two 

 regular longitudinal rows as shown in figure, and their shape is also slightly altered. 

 Papulae arc tlistributed all over the abactinal surface, as is characteristic for this 

 genus. They are usually in sixes about each plate, and are never more than one to 

 an area on cither side of the mid-radial scries of plates, as is the case in D. eximius at 

 about the middle of the ray. 



The arrangement of the midradial row of plates and adjacent papulae, as well as 

 the form of plate, and their size toward center of disk, constitute some of the most 

 reliable differences between this s{)ecies and eximius. These are best shown by 

 the figures (pi. .52, figs Ic, 2h). 



Marginal plates massive, the inferomarginals defining the margin of ray when 

 viewed from above. Superomarginals, thirty-four in number from interradial line, 

 are wider than long and form a slightly arched bevel to abactinal surface. They 

 are not quite so strongly arched as those of D. exiinius, nor are the plates so tumid; 

 and in proportion to length are a trifle wider. The plates are covered with low, 

 flat-topped dose-set hexagonal and pentagonal granules, largest near center or 

 upper end, becoming slenderer toward edge of plate, where they assume the form 

 of robust, blunt spinelets, never slender and sharp as in eximius. Beyond middle 

 of ray on each plate one to three granules are usually enlarged into short, bluntly 

 pointed tubercles, and are situated on aboral edge of plate, being directed toward 

 edge of ray. On the more distally situated plates the granules increase in size 

 toward this tubercle, which increases in length toward the end of ray but is never 

 conspicuous. The aboral transverse edge of the specialized ridge of plate becomes 

 in this region slightl}- more abrupt than the adoral edge which is rounded. This is 

 due to the crowding of the large granules toward the aboral edge. The whole 

 covering of the plate is more compact, firm, and graniliform than in eximius. The 

 fasciolar grooves between the plates (or specialized ridges of them) are not so broad 

 as in eximius, and unlike the latter species, are not evident unless the plate is 

 denuded. 



Inferomarginals correspond to superomarginals and encroach conspicuously 

 onto actinal area, about wliich they form a slightly arched border, the outer ends 

 forming a rounded serrate edge to ray. The sjiecializeil ridge of each plate, when 

 denuded, is much thicker than the adjacent furrows, and is relatively thicker 

 and the furrows are relatively much narrower than in eximius. The plates are 



