146 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



median keel. The IBr 2 (axillaries) are slightly longer than broad, shield-shaped, with 

 the proximal border produced into a rounded projection incising the IBri, the anterior 

 edges concave, the anterior angle somewhat produced, and the lateral edges somewhat 

 denticulate ; there is a sharp serrate median keel in the proximal two-thirds. The IIBr 

 series are 4(3+4), rarely 2, and are strongly convex dorsally; they are in close lateral 

 apposition and are sharply flattened laterally, like the IBr series; the lateral edges are 

 produced and strongly denticulate. The syzygial pair formed by the two outer elements 

 is centrally constricted with the lateral angles produced as in the other species of the 

 genus. 



The 20 arms are 115 mm. long. The first brachials are short, slightly longer ex- 

 teriorly than interiorly, interiorly united, and somewhat incised by the second, which are 

 nearly twice as large and have a rounded posterior projection. The first and second 

 brachials, like the two elements of the IBr series, have a slightly marked median can- 

 nation. The first syzygial pair (composed of brachials 3+4) is not quite so long as 

 broad and is somewhat constricted centrally. The next five or six brachials are almost 

 oblong, about twice as broad as long, with the dorsal profile rather strongly concave. 

 The brachials following become wedge-shaped and soon triangular, nearly as long as 

 broad, and after the middle of the arm wedge-shaped again and about as long as broad. 

 At first the arms are evenly rounded dorsally, but after the basal third they gradually 

 become compressed and more sharply rounded dorsally, and in the outer half very 

 narrow and very sharply rounded dorsally, though not really carinate. After the basal 

 third of the arms the brachials develop slightly projecting and finely spinous distal edges. 

 The dorsal, but not the dorsolateral, side of the fourth and following brachials is covered 

 with fine short spines which gradually become coarser after the proximal third of the 

 arm and tend to arrange themselves in longitudinal lines. The ossicles of the division 

 series and arm bases have strongly denticulate borders. 



Syzygies occur between brachials 3+4, again from between brachials 25+26 to 

 between brachials 35 + 36 (usually in the vicinity of the twenty-ninth), and distally at 

 intervals of from 5 to 17 (usually from 7 to 9) muscular articulations. 



P D 12 mm. long, moderately stout in the proximal half but becoming slender distally, 

 with about 20 segments all of which are approximately as long as broad, those in the 

 basal two-thirds being strongly carinate. P! 10 mm. long, similar to P D but less stout 

 basally. P 2 6 mm. long, much more slender than PI, tapering evenly from the base to 

 the tip, with 15 segments of which the proximal four or five are about as long as broad, 

 those following becoming longer than broad and about twice as long as broad terminally. 

 P 3 is similar, 6 mm. long. P 4 and the following pinnules are 5 mm. long with about 13 

 segments, less slender distally than those preceding; the segments have slight over- 

 lapping spines developed on the distal edge along the dorsal crest. The distal pinnules 

 are 10 mm. long, rather slender, composed of about 20 segments of which the first is 

 short and crescentic, the second is trapezoidal and about as broad distally as its median 

 length, and those following are half again as long as broad, with the terminal four or 

 five disproportionately small; the dorsal crest is sharp and somewhat spinous. 



The perisome over the gonads is encased in well-formed and definite plates of very 

 different sizes and shapes some of which, near the borders of the piunulars, are longi- 

 tudinally elongated. The side- and covering-plates resemble those of 0. gigantea. 



