8 BULLETIN 115, UNITED STATES NATIONAL 'MUSEUM. 



with a much greater extent of incoiporation of brachials by means of 

 the fixed pinnules. The broadly rounded secundibrachs are strongly 

 arched exteriorly, and are deeply V-shaped on the ventral side, the 

 wings of the V being further prolonged by the pinnules, the lower 

 ossicles of which form a continuous wall in the depressed interbrachial 

 areas. These give the appearance of numerous iBr plates above the 

 very large first interbrachial; but in fact the interbrachials are limited 

 to a single narrow plate following the first, or two in linear series, 

 the second of which may not reach to the exterior, while the other 

 rather numerous plates in the area are all pinnulars. In this way 

 secundibrachs to the height of the seventh are incorporated. IlBr2 

 has a ])innule to the outside of the dichotom, and IlBr^ has one to 

 the inside, neither of them showing externally (except at the margin), 



with 8 or more pinnule-ossicles incorpo- 

 rated. IIBr^ to IIBrg have from 2 to 4 

 pinnules to each brachial, with 2 or more 

 pinnulars incorporated. The reduced first 

 ]irimibrach occupies an oval space be- 

 tween the radial and the axillary IBr, 

 both of which are more or less excavated 

 for its reception. It is usually small, 

 strongly protuberant, and the radial ridge 

 Fi<:. 2.- PINNULES OF coMANTno- followiiig thc rays begins with this plate. 

 ^^^^^'^- The anal side is scarcely differentiated, 



two narrow plates tandem succeeding the large first plate and 

 passing toward the tegmen, which is not preserved in any of our 

 specimens. 



The inside of the dorsal cup is marked by an extraordinary com- 

 plex of grooves and ridges from the basals and radials up, which are 

 doubtless for the lodgement of nerve cords, but the exact function of 

 so many is not clear. They are comparable in number and position 

 with the ridges and furrows seen upon the dorsal side of calyx plates 

 in well-preserved specimens of Ilimeroennus iitlenissi'mufi , but nothing 

 so intricate has been observed upon the inner surface in other forms. 

 A few sharp nodes appear at the exterior on radials and interbrachials. 

 Most of the material is in poor condition, but we are fortunate in 

 having two specimens which, except for the lack of the tegmen, are 

 remarkably well preserved for exhibiting the essential characters of 

 the species; in one the dorsal and ventral surfaces are completely 

 exposed, and in the other the ventral side only. By means of these 

 we are able to illustrate both aspects of the calyx, and to show the 

 actual relations of the incorporated plates by diagrammatic sketch, 

 as well as by direct drawings. SeA'eral other fragmentary specimens 

 confirm the description in various particulars. 



