A MONOGRAPH OF THE EXISTING CRINOIDS 447 



the third segment is longer than the first two, about half again as long as broad. P a 

 is similar to P, but somewhat shorter and smaller. P 2 is 8-16 (usually 10-15) mm. 

 long, with 9-1 S (usually 12-16) segments, stiffened and rigid, spinelike, and sharp 

 pointed, usually straight though sometimes more or less strongly curved outward 

 toward the arm tip, usually stout, sometimes very stout, more rarely rather slender. 

 It is longer and much stouter than P, and tapers more gradually. It is frequently, 

 though not always, markedly longer and stouter on the outer arms of each postradial 

 series than on the inner arms, the corresponding pinnule on the inner arms being of the 

 same size as P a or somewhat smaller. The first two segments vary from broader than 

 long to about as long as broad, the third varies from the same length as the first two 

 to about twice as long as broad, and those following are greatly elongated, usually 

 about three times as long as broad or even longer, the fourth and fifth being more or 

 less markedly longer than the others, though sometimes the longest segments are the 

 eleventh and twelfth. Usually the ends of the elongated segments are slightly swollen. 

 P b is similar to P 2 but shorter. P 3 is usually scarcely half as long as P 2 , small, weak, and 

 flexible, 4-7 (commonly about 5) mm. long, with 8-15 (usually 10-12) segments. The 

 three or four pairs of pinnules following are similar, after which the pinnules slowly 

 increase in length, the slender distal pinnules being 8 or 9 mm. long. 



The disk is 11-15 mm. in diameter and is naked and moderately to strongly 

 incised. The ambulacral grooves have lines of sacculi along their sides, which become 

 very prominent toward the margin of the disk and give off branches to the first pair of 

 pinnules. Along the ambulacral grooves of both arms and pinnules the sacculi are 

 large, abundant, and closely set. 



Notes.- — The specimen from Macclesfield Bank is small, with the arms 65 mm. 

 long; P 2 has 13 segments. 



The specimen from Challenger station 208 served Carpenter as the basis for the 

 description of his new species Antedon marginata. Carpenter said that the centrodorsal 

 is saucer-shaped. The cirri are XXV, 20. A few of the segments are somewhat longer 

 than broad, and the terminal are rather compressed laterally, having a faint keel that 

 passes into the dorsal spine of the penultimate — -that is, the opposing spine. The 

 radials are just visible beyond the rim of the centrodorsal. The IB^ are oblong and 

 are quite free laterally. The IBr 2 (axillaries) are pentagonal and about half again as 

 long as the IBr^ The IIBr series are 2. The IBr and IIBr series are rather convex, 

 rising sharply to the middle of their apposed edges — that is, synarthrial tubercles are 

 present. The ventrolateral borders of all the ossicles from the. IBr! to the second 

 brachials inclusive are marked by irregular projections toward the ventral side. The 

 14 arms are 100 mm. long and consist of about 150 brachials, of which the lower are 

 thick disks and their successors are more triangular, though wider than long, gradually 

 becoming quadrate and more discoidal again in the middle of the arm. Syzygies occur 

 between brachials 3+4, again from between brachials 9 + 10 to between brachials 

 14+15, and distally at intervals of from 4 to 7 muscular articulations. 



Pi is comparatively slender and consists of about 20 segments, most of which are 

 longer than broad. P a is similar, but smaller. P 2 and P b are not much longer than the 

 pinnules of the first pair, reaching 10 mm. in length, but they have only 10-12 very 

 stout and rather elongated segments, which terminate somewhat abruptly. P 2 is 

 larger than P b . P 3 and P are of the same character as P 2 and P„, but less stout, though 



