A MONOGRAPH OF THE EXISTING CRINOIDS 219 



radial angles, where they are separated by narrow grooves. The IB^ are very short, 

 from five to sLx times as broad as long, with the proximal and distal edges somewhat 

 swollen. The IBr 2 (axillaries) are rhombic, twice as broad as long. There is a promi- 

 nent high and narrow synarthrial tubercle on the articulation between the elements 

 of the IBr series. The IBr series are broad and are almost or quite in lateral contact. 



The 10 arms are 60 mm. long. The first brachials are wedge-shaped with the 

 exterior length about twice as great as the interior, nearly three times as broad as the 

 exterior length, interiorly united for almost their entire length. The second brachials 

 are of about the same size, with the ends slightly more oblique. There is a prominent 

 synarthrial tubercle on the articulation between the first two brachials, the lower 

 element of which, on the first brachial, is very broad. The first syzygial pair (com- 

 posed of brachials 3+4) is nearly twice as broad as the median length, and is slightly 

 longer interiorly than exteriorly. The next five brachials are nearly oblong, between 

 three and four times as broad as long, those following becoming sharply triangular, 

 half again as broad as the greatest length, with the distal ends somewhat produced and 

 finely spinous. In the outer half of the arm the brachials become wedge-shaped and 

 very slowly elongate, so that those at the arm tip are as long as, or slightly longer than, 

 broad. 



Syzygies occur between brachials 3+4, again from between brachials 14 + 15 to 

 between brachials 24+25 (most commonly between brachials 16+17), and distally at 

 intervals of from 5 to 10 (most commonly 6 to 8) muscular articulations. 



P! is 4.2 mm. long, tapering more rapidly in the proximal than in the distal half, 

 rather strongly prismatic, with 16 segments. The first segment is short, about three 

 times as broad as long in the median line, with the proximal border in the form of an 

 obtuse angle, the distal border straight, and the short lateral borders convex. The 

 second segment is about twice as broad as long, and is oblong. The segments following 

 gradually increase in length so that the outermost are about twice as long as broad. 

 The second segment has a broadly rounded prismatic ridge. On the segments follow- 

 ing this rapidly becomes narrower and soon very narrow, the outer half of the pinnule 

 being much flattened. In the outer half of the pinnule the side toward the arm tip is 

 serrate, the ends of the segments along the prismatic ridge projecting beyond the 

 bases of the segments succeeding. P 2 is 5.8 mm. long, much larger and stouter than P! 

 and tapering more gradually, strongly prismatic, with 14 segments of which the first is 

 about twice as broad as long with the proximal border forming an obtuse angle of 

 about 120, the distal border straight, and the short lateral borders somewhat convex. 

 The second segment is oblong, about twice as broad as long. The segments following 

 slowly increase in length so that the outermost are about twice as long as broad. The 

 central portion of the outer side of the third segment is broadly raised. On the seg- 

 ments following tliis elevation of the central portion rapidly becomes sharp so that 

 from the fifth onward the segments are strongly flattened with a sharp prismatic 

 ridge. On the third and following segments the outer portion of the prismatic ridge is 

 produced outward so that the distal ends of the segments at the prismatic' ridges 

 extend considerably beyond the bases of the segments following, giving the pinnule a 

 serrate profile. These extensions of the prismatic ridge usually bear a few coarse 

 teeth. P 3 is 3.9 mm. long with 14 segments, less stout basally than P 2 and becoming 

 slender in the distal half. The first segment is between two and three times as broad 



