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long, broadly V-shaped in direct lateral view, with the proximal and distal edges parallel ; the 
proximal and distal edges are slightly everted ; the former bears a few short irregularly placed 
spines on the margin ; the latter bears on either side of the median line about eight regular 
teeth which begin one third of the distance from the median line and gradually increase in 
length to the lateral corners; this row of teeth is continued inward toward the median line by 
small spines of decreasing size ; the lateral edges are slightly produced and smooth ; the antero- 
lateral angles bear a few prominent blunted spines; there is a prominent and sharp, though 
not especially high, median keel. The IBr, (axillaries) are broadly rhombic, with the lateral 
angles truncated, about twice as broad as long; the lateral edges, which are not quite so long 
as those of the IBr^, are produced and irregularly and coarsely spinous; the distal edges and 
the outer portion of the proximal edges are slightly everted and finely spinous; a prominent 
keel, resembling that on the IBr^, runs nearly their whole length. IIBr 4 (3 -)- 4) (nine present), 
resembling the IBr series and, like them, prominently carinate ; the lateral borders of the 
elements of the IIBr series are produced and irregularly denticulate or spinous. IIIBr 4 (3 -f 4) 
(nine present), resembling the IIBr series; the ossicles of the division series and of the arm 
bases have produced and irregularly denticulate lateral borders as far as the base of P, externally, 
and as far as the fifth or sixth brachial internally. 
The arms are 28 in number, about 120 mm. long, resembling those of O. giga7itea\ 
the first two brachials are carinate; the following have slightly everted and finely spinous distal 
edges, and the dorsal (but not the dorsolateral) surface covered with very numerous short fine 
spines; as the brachials become triangular the proximal edges gradually lose their eversion, 
while that of the distal edges becomes • recumbent and more prominently spinous, and the 
spinosity of the dorsal surface gradually becomes arranged in definite lines, becoming a series 
of sharp serrate longitudinal striations. 
The disk, especially along the ambulacral grooves, is thickly beset with small rounded 
plates which become produced along the ambulacra ; side and covering plates are well developed. 
Pd is from 14 mm. to 16 mm. long, composed of 28 — 30 segments, comparatively 
slender as in the two other species of the genus, and tapering very gradually to a delicate 
tip; all of the component segments are broader than long; the distal outer and distal inner 
margins of the segments are sharply and verj- prominently qarinate, this carination being very 
spmous, and on the proximal portion of the inner margin coarsely denticulate; a shallow concave 
through runs between these ridges; the proximal segments are mere or less spinous on the 
proximal (dorsal) surface. Pp is like Pd, but not nearly so long nor so large. Pj is 14 mm. 
long with 26 segments, similar to Pd but more slender with the component segments somewhat 
longer and their produced borders more spinous, and the distal edges of the outer produced 
and spinous. Pj, is 8 mm. long with 17 segments, much more slender than Pj wnth longer 
segments distally which have more produced and spinous distal edges. The following pinnules 
become progressively more slender with progressively longer segments which have coarsely 
spinous distal ends. P,, is 7.5 mm. long; P^ is 7 mm. long; P. is 6.5 mm. long; P^ is 6 mm. 
long. The distal pinnules are 13 mm. long, composed of 18 — 20 segments; the crest of the 
prismatic ridge is finely spinous. 
