144 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



IBr2 and the elements of the IIBr series are rounded dorsally and laterally, and 

 entirely free laterally. The synarthrial tubercles are broad and low, though rather 

 noticeable. 



There are 19 arms in the type specimens of ornata, which are about 120 mm. 

 long. The first 2 brachials are similar in size and shape, slightly wedge-shaped with 

 the longer side outward, and about twice as broad as the exterior length. The first 

 brachials, like the IIBr,, are united interiorly for nearly their entire length. The 

 second, like the IIBr2, are usually interiorly in apposition with their neighbors, though 

 not united to them. The first syzygial pair (composed of brachials 3 +4) is about as 

 long as broad. The fifth and sixth brachials are oblong, about twice as broad as 

 long, and those following become very oblique and after the eighth or ninth triangular, 

 about as long as broad, later wedge-shaped, and somewhat less oblique distally. The 

 terminal portion of the arms is not preserved. The elements of the IBr and IIBr 

 series and the first 2 brachials have the dorsal surface thickly covered with small 

 shallow pits. The distal edge of the second brachial is everted and somewhat promi- 

 nent, tending to form a rounded distal dorsal prominence which is thickly beset with 

 small spines. This condition rapidly becomes intensified distally, the brachials after 

 the eighth having strongly produced distal ends which are armed with a frill of rather 

 coarse spines, these produced distal ends standing out nearly perpendicularly to the 

 axis of the arm. With the gradual narrowing of the arm distally this eversion of the 

 distal ends of the brachials gradually narrows, but does not increase in height, so 

 that on the later brachials it appears as a laterally oblong distal tubercle with the 

 summit thickly studded with small spines standing vertically outward and reaching 

 in height rather more than half the ventrodorsal width of the brachials. In lateral 

 view these tubercles appear as rounded distal spines, the general effect being the 

 same as in the more cariuate varieties of Tropiometra pida. 



Syzygies occur between brachials 1+2, and always between brachials 3 + 4; the 

 next syzygy from between brachials 13 + 14 to between brachials 18 + 19, though it 

 is mostly between brachials 17 + 18. The distal intersyzygial interval appears to be 

 from 6 to 8 muscular articulations. The sj^zygies are exceedingly difficult to detect, 

 as the perisome covering the dorsal surface of the brachials is somewhat swollen and 

 opaque, thus masking the structure beneath. 



Pi is about 15 mm. long, much stouter basally than those succeeding, but taper- 

 ing with moderate rapidity and slender and flagellate in its distal two-thirds. It is 

 composed of about 40 segments, which at first are about twice as broad as long, more 

 or less rhombic with the corners cut away, but become about as long as broad and 

 squarish after the tenth. The terminal comb is long and arises gradually; it is com- 

 posed of 25 teeth, which at first are low and after the fifth become bluntly triangular, 

 higher than broad at the base, about as high as the lateral width of the segments 

 bearing them; their apices lean somewhat distally. In the distal part of the pinnule 

 the shape changes somewhat, the last 9 teeth being much more rounded distally, 

 erect, and slightly shorter. The teeth are slightly recurved. Pa is 8 mm. long, 

 much more slender than Pj basally and with fewer segments, but otherwise similar 

 to it and with a similar comb. The following pinnules gradually decrease in length 

 to Pe which is 6 mm. long with a rather small comb. P, is rather stouter than Pj, 



