406 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



sides of about the same length which are less than half as long as the inner edge of the 

 IIBr,. The distal edges are gently concave and the anterior angle is approximately 

 a right angle. The IIIBr series resemble the IIBr series, but the component segments 

 are relatively longer. All the IIIBr series are developed externally. 



The 23 (5 + 6+4+4 + 4) arms are 80 mm. long from the radials. The first 

 brachials are half again as long exteriorly as interiorly, and about twice as broad as 

 the median length. The proximal edge is gently convex and the distal edge is much 

 more strongly concave. The outer and inner edges are straight and the latter are in 

 close contact with the adjacent first brachials. The outer sides are sharply and 

 rather broadly flattened. The second brachials are of about the same size as the 

 first, but the distal edge is straight and at right angles to the longitudinal axis of the 

 arm, and the proximal edge is strongly convex. The first syzygial pair (composed of 

 brachials 3 + 4) is from half again to about twice as broad as long, with the proximal 

 and distal edges parallel; the hypozygal is usually slightly larger than the epizygal. 

 The next two brachials are oblong, between three and four tunes as broad as long, 

 after which the brachials become wedge-shaped and almost immediately triangular, 

 more than twice as broad as the length of the longer edge. After the middle of the 

 arm the brachials again become wedge-shaped and slowly elongate so that distally 

 they are about as long as broad. The terminal three or four brachials are very small, 

 without pinnules, and are recurved ventrally between the outermost pinnules which 

 extend for 3 mm. or more beyond them. In the basal portion of the arms the dorsal 

 surface is broadly and evenly rounded. After about the fifteenth brachial the central 

 portion of the dorsal surface gradually begins to rise, soon becoming a gablelike 

 ridge. As the arm gradually becomes compressed laterally this ridge rises into a 

 carination that develops into a high, broad, curved spine the distal end of which 

 overlaps the base of the succeeding brachial. 



The distribution of the syzygies is irregular. The first syzygy is usually between 

 brachials 3+4, but may be between brachials 4 + 5 or 5 + 6, or even as far out as 

 18 + 19. The second syzygy is from between brachials 12+13 to between brachials 

 20 + 21. The distal intersyzygial interval is from 3 to 7, usually 5 or 6, muscular 

 articulations. 



P! is 6.5 mm. long with 11 segments, tapering rather rapidly in the first four, 

 thence much more gradually. The first segment is more or less semicircular, somewhat 

 broader than long. The second is slightly broader than long and tapers slightly 

 distally. The third is longer than broad and tapers distally. The fourth is twice as 

 long as the median width with the distal end somewhat more than half as broad as the 

 proximal. The following segments are cylindrical, from two and one-half to three 

 times as long as broad except for the terminal, which is a mere button. P 2 is 11 mm. 

 long with 14 segments and tapers evenly and slowly from the base until near the tip. 

 The first segment is nearly twice as broad as long, the second is about as long as broad, 

 the third is very slightly longer than broad, and those following very slowly increase 

 in length so that the twelfth is about twice as long as broad and the thirteenth some- 

 what longer and tapering distally. The terminal segment is minute. From the third 

 onward the segments are sharply triangular hi cross section so that the pinnule shows 

 a sharp ridge or crest along the outer side. P 3 is 11.5 mm. long with 14 segments and 

 resembles P 2 . P 4 is 11 mm. long. P 6 is 10 mm. long. P 8 and P 7 are 10.5 mm. long. 



