A MONOGRAPH OF THE EXISTING CRINOIDS 179 



the terminal sometimes broader than long; the dorsal pairs of tubercles on the distal 

 segments are often indistinct or more or less fused; P 2 is markedly longer than P t or 

 PS with 12-20 segments of which the outer are not more than twice as long as broad 

 with somewhat overlapping and spinous distal ends; the lower pinnules are stiffened; 

 the arms are 40-80 mm. long. 



Description. The centrodorsal is discoidal, thin, with a rather large bare polar 

 area about 2 mm. broad that is broadly and slightly elevated centrally and also per- 

 ipherally. The cirrus sockets are arranged in a single or partially double marginal 

 row. 



The cirri are XVIII-XXX, usually 20, 10 mm. long. The first segment is short, 

 from three to four times as broad as long, the second is from two and one-half to three 

 times as broad as long, and the third is about twice as broad as long or a little broader. 

 The segments following slowly increase in length so that the seventh or eighth and those 

 succeeding are about as long as broad, or sometimes slightly longer than broad termi- 

 nally. On the second segment the entire distal dorsal edge is slightly produced and 

 finely serrate. This production of the distal dorsal edge slowly increases and on the 

 sixth or seventh becomes somewhat higher at the two ends than in the middle, the 

 crest being slightly concave, and at the same time moves proximally from the end of 

 the segments. From this point onward the transverse ridge shortens and at the same 

 time moves more and more proximally so that on or about the twelfth segment it be- 

 comes a very short median transverse ridge, usually more or less distinctly divided 

 into two tubercles, and on the last three to five or six segments before the penultimate 

 becomes a small median dorsal tubercle or blunt spine. The opposing spine is much 

 larger than the spines on the segments preceding, triangular, sharp and erect, arising 

 from the central half of the penultimate segment, and equal in height to from one- 

 third to one-half the width of that segment. The terminal claw is about as long as the 

 penultimate segment, and is stout and strongly curved. 



The radials are usually concealed by the centrodorsal, more rarely just visible in 

 the interradial angles of the calyx. The IBrj are somewhat over twice as broad as 

 long, well rounded dorsally and well separated laterally. The IBrj (axillaries) are 

 pentagonal, over twice as broad as long. There is a slightly developed synarthrial 

 tubercle. 



The 10 arms are from 40 mm. to 50 mm. long. The first brachials are wedge- 

 shaped, with the shorter side in, and are almost completely united interiorly. The 

 second brachials are almost oblong. The first syzygial pair (composed of brachials 

 3+4) is about as long as broad. The next 2 brachials are oblong, not so long as broad, 

 and those succeeding become wedge-shaped and after the eighth triangular, nearly 

 as long as broad, in the distal portion of the arm gradually becoming wedge-shaped 

 again and elongate distally. From the eighth onward the brachials have abruptly 

 everted distal ends which stand out at right angles to the axis of the arm and are 

 furnished with a rather broad border of fine spines; this feature gradually dies away 

 in the distal portion of the arm. 



Syzygies occur between brachials 3+4, 9 + 10 and 14+15, and distally at inter- 

 vals of 4 muscular articulations. 



P 8 is absent. P] is 5 mm. long, slender and tapering gradually from the base to the 

 tip, with 13 segments of which the first 3 or 4 are about as long as broad and those 



