352 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Description. The centrodorsal is large, up to 9.25 mm. broad at the base and about 

 7 mm. high, hemispherical with the dorsal pole flattened and sometimes more or less 

 excavated and the surface elsewhere covered with closely crowded cirrus sockets 

 which show no regular arrangement. 



The cirri are LXXX-C, 40-60 (usually 45-55), the longest marginal from 55 mm. 

 to 91 mm. long (usually between 60 and 70 mm.) and rather stout. The first four 

 segments are very short, the following increasing in length to about the ninth or even to 

 the thirteenth, which are from one third to one half again as long as broad, and then 

 gradually decreasing so that those in the distal third of the cirri are somewhat broader 

 than long. The short distal segments are slightly compressed laterally with a more 

 or less sharpened median dorsal edge and their dorsal profile distally diverges slightly 

 from the ventral, which is parallel with the longitudinal axis, so that the median portion 

 of the dorsal end of each is higher than the base of the next succeeding, causing the 

 dorsal profile of the distal portion of the cirrus as a whole to appear more or less 

 distinctly serrate. 



In any one specimen only relatively few of the cirri are of this type, the majority 

 being shorter with fewer segments, regularly decreasing in length and in the number 

 of the component segments from the margin of the centrodorsal to the region immedi- 

 ately about the dorsal pole. 



The distal dorsal border of the radials is even with the edge of the centrodorsal 

 throughout most of their width, but the distal corners are visible in the interradial 

 angles. The IBr : are very short, the median portion in lateral view being concealed by 

 the rounded posterior projection of the axillary, and their sides are almost or quite in 

 contact with those of their neighbors basally, diverging distally. The IBr 2 (axillaries) 

 are typically rhombic with the proximal angle more or less rounded and the distal 

 angle acute and about as long as broad. However, they vary considerably in shape 

 from rhombic to triangular, according to the extent of their posterior projection into 

 the IBr t ; they may be somewhat longer than broad, but in most cases their width is 

 equal to or slightly greater than the length, more than half of which is on the distal 

 side of the line joining the lateral angles. 



The 10 arms reach a length of from 240 to 265 mm. and are composed of more than 

 300 brachials. The first brachial is very short, twice as long outwardly as inwardly, 

 deeply incised in the median line by a rounded posterior projection from the second, 

 which is much larger and irregularly quadrate. The third and fourth brachials form 

 together the first syzygial pair which is from half again to almost twice as broad as 

 long. The following brachials are wedge-shaped, about twice as broad as the median 

 length, after the second syzygial pair quickly becoming triangular, usually broader 

 than long, sometimes about as long as broad, and distally wedge-shaped again and 

 gradually elongate. 



On the articulations between the earlier wedge-shaped brachials at the base of the 

 arms, the region immediately adjacent to the ends of the apposed fulcral ridges is pro- 

 duced into a series of more or less prominent pointed tubercles, which alternate in 

 position, giving the arm bases a singularly rugged appearance. 



Syzygies occur between brachials 3+4, 9 + 10, 14 + 15 and distally at intervals of 



3 or 4 (most commonly 4) muscular articulations. When the first syzygy is about 



4 mm. wide the length from the proximal edge of the IBr t to the second syzygy is 18 



