112 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



The ambulacra] grooves themselves are bordered with large regular plates. The 

 plating on the brachial and pinnule ambulacra is very highly developed. The perisome 

 of the arms is completely covered with rather large plates so that the arms and pinnules, 

 when the covering plates are closed down, are completely encased in a calcareous 

 cm ering. 



The ends of the basal rays arc visible as small, though prominent, tubercles in 

 the intexradial angles of the calyx, 



The radials are of uniform width all around the calyx, short, somewhat over four 

 times as broad as long, with the distal border set with small scattered spines. The 

 lBr; are short, of uniform height, with the proximal border convex and the distal 

 concave, about three times as broad as long; the proximal edge is slightly prominent, 

 and the lateral edges arc in very close apposition and rather prominently everted, the 

 ircst of the resultant ridge being finely spinous. The IBr 2 are broadly pentagonal, about 

 twice as broad as long, with the lateral edges about as long as those of the IBri and 

 everted and finely spinous like those of that ossicle. Like the IBn and the first two 

 brachials it bears a single small but rather prominent rounded tubercle near each 

 lateral margin. 



The 10 arms are stout and rugged but becoming slender distally, 150 mm. in length. 

 The first brachials are longer exteriorly than interiorly, with the distal border concave, 

 the interior edges closely united, and the exterior edges everted and spinous like the 

 lateral edges of the preceding ossicles. The second brachials are about twice as large 

 as the fust, irregular in shape, with the proximal border strongly convex; they are in 

 close apposition with their neighbors and strongly flattened against them, and both the 

 exterior and interior edges are everted and spinous. The first syzygial pair (composed of 

 brachials 3 + 4) is half again as broad as long, laterally flattened both exteriorly and in- 

 teriorly, with the lateral edges less strongly everted than those of the preceding ossicles. 

 The succeeding five brachials are approximately oblong, about 3 times as broad as 

 long and rather strongly tubercular, those after the twelfth becoming triangular and 

 about as long as broad, this proportion remaining unchanged until near the arm tips 

 v. here the brachials become wedge-shaped and somewhat longer. The distal edges 

 of the brachials in the outer two- thirds of the arms arc overlapping and finely spinous. 



Syzygies occur between brachials 3 + 4, again from between brachials 14+15 to 

 between brachials 17+18, and distally at intervals of from 4 to 10 (usually 6 or 7) 

 muscular articulations. 



i', is large and very stout, strongly flattened exteriorly, composed of 17-18 seg- 

 ments all of which are broader than long; the pinnule tapers rather rapidly after the 

 proximal third so that the terminal portion is delicate with very small segments. P 2 

 is 7 nun. long, stout basally, though not nearly so stout as Pij it tapers rapidly, so 

 that the distal half is slender, and is composed of 14 segments of which the first 3 are 

 broad, the fourth is about as long as broad, and the remainder are somewhat longer 

 than broad. The first 6 segments of P] have the distal side very strongly concave, 

 forming 2 sharp keels, one external along the flattened outer side, the other internal; 

 the external keel is armed with tine spines. The distal segments are prismatic, with 

 i lie angles somewhat produced. Pj has a similar double carination but, while the 

 exterior keel is much lower, it persists in a raised and very spinous line to the tip of the 

 pinnule; the ends of the distal segments are much more spinous than is the case in 



