A MONOGRAPH OF THE EXISTING CRINOIDS 363 



swollen and more or less prominent distal ends. The cirrus segments are usually 

 subequal. the difference between the longest proximal and the others being Blight. 

 Somewhere between the tenth and the twenty-first segment the first dorsal spine 

 appears. The dorsal spines are usually large, broad, and prominent, arising from the 

 entire dorsal surface of the segments, though they may be smaller and lower, confined 

 to the distal portion of the segments and in height not exceeding one-tliird their width. 

 They are directed obliquely forward, except for the one or two preceding the opposing 

 spine, which are smaller than the others and erect. Occasionally a few of the earlier 

 spines are transversely elongated, or they may be double, there being two spines 

 situated side by side. More rarely the two to eight spines following the first three or 

 four have a longitudinally elongate chisellike crest, or there may be two spines, one 

 in advance of the other. The opposing spine is much larger than the spines on the 

 segments immediately preceding; it is erect and arises from almost the entire dorsal 

 surface of the penultimate segment. The terminal claw is half again as long as the 

 penultimate segment and is slender distally and strongly curved. 



The radials are almost or quite concealed; if visible they are smooth and very 

 short, longest in the interradial angles. The IBr, are very short and are almost or 

 quite united laterally. The IBr 2 (axillaries) are almost triangular, twice as broad as 

 long, and are not quite in lateral contact. The division series and earlier brachials 

 are usually more or less flattened laterally. More or less strongly developed synar- 

 thrial tubercles are usually present. These are conical and sharp and arise abruptly. 

 Rarely IIBr 2 series occur; one IIBr 3 series has been noted. 



The 10 (rarely 11 or 12) arms are in full-grown individuals 115 to 300 (most 

 commonly between 150 and 225) mm. long. The first brachials are interiorly united, 

 and the first four brachials are more or less flattened laterally. The brachials to 

 about the tenth are discoidal, smooth, with more or less marked dorsolateral swellings. 

 After the tenth they become more or less triangular, and soon discoidal and extremely 

 short with the finely spinous distal ends slightly produced and overlapping. 



Syzygies occur between brachials 3+4, 16 + 17 to 21+22 (usually 18+19), and 

 25+26 to 32+33, and distally at intervals of 6-12 (rarely as many as 17) muscular 

 articulations. 



Px is 5.5-13 (most commonly about 8) mm. long, with 13-22 (usually 13-18) 

 segments. It is markedly smaller than P 2 and P 3 and is more slender distally. It is 

 smooth, and the earlier segments are triangular in cross section. From the third 

 onward the segments, except the distal, are a little longer than broad; the outermost 

 have the distal edge slightly produced. P 2 resembles P, but is longer and stouter, 

 7-16 (usually 9-11) mm. long, with 13-22 (usually 16-20) segments, of which the first 

 is short and squarish and the third and fourth are commonly the longest ; the second- 

 sixth are triangular in cross section. P 3 resembles P 2 and is usually of the same 

 length, though sometimes slightly shorter. P 4 is shorter than P 3 , with about the 

 same number of, or slightly fewer, segments. The pinnules following are shorter 

 and slenderer, with shorter segments. The distal pinnules are 6.5-9 mm. long, with 

 16-23 (usually 18-20) segments, of which the first two are broadened and swollen, 

 and those from the ninth onward are long and slender. Some of the lower pinnules 

 may have a trace of carina tion, usually only on the lower segments. 



