A MONOGRAPH OF THE EXISTING CRINOIDS 75 



is somewhat flattened exteriorly; the segments have finely serrate distal edges and the 

 distal outer angle may be somewhat produced. P 2 resembles PI but is slightly shorter 

 and less stout. The pinnules following decrease gradually in length to about P 6 , which 

 is 4 mm. long with 9 segments, all broader than long except the last two. The genital 

 pinnules increase slowly in width from the base to the third segment, thence tapering 

 to the tip, the second and third, or second- fourth segments being slightly broadened. 

 The distal pinnules are more slender, 7 or 8 mm. long with 18 segments, all of which are 

 about as long as broad and very sharply carinate. 



The disk is moderately or well plated, and the ambulacra are well plated. Sacculi 

 are abundant on the pinnules. 



A T otes. In other specimens from the type locality the proximal, distal, and lateral 

 borders of the elements of the IBr series and the lateral borders of the IIBr series may 

 be more or less extensively irregularly tuberculate, this tuberculation sometimes 

 involving the entire dorsal surface of the IBrj, and some specimens show a very distinct, 

 though low and narrow, middorsal line on the division series and on all the brachials 

 of the proximal portion of the arms. 



Gislen's original description of Perissometra aranea based upon a single specimen 

 from Bock's station 7a is as follows: The centrodorsal is a low cone 2 mm. in diameter, 

 dorsally with a central cavity and small side cavities. The cirrus sockets are arranged 

 in 10 columns, one or two in each column. 



The cirri are XIV, 17-21, 10-11 mm. long. The first-third segments are broader 

 than long, the fourth is somewhat longer, the fifth is half again as long as broad, and the 

 sixth is twice, as long as broad, distally a little widened and with an inconspicuous 

 dorsal spine. The segments following are shorter, each with a dorsal spine. From 

 about the ninth the segments are about as long as broad; the antepenultimate is half 

 again as long as broad. The opposing spine reaches a height of about one-fifth of the 

 penultimate segment. The terminal claw is curved and is somewhat longer than the 

 segment preceding. 



The radials are in the form of narrow bands, almost concealed. The IBri are 

 four times as broad as long with a low median carination and are in lateral contact. 

 The IBr 2 (axillaries) are pentagonal, three times as broad as long, with a similar low 

 longitudinal tubercle. There is a slight thickening of the distal border, the rest of the 

 ossicle being smooth. It is laterally flattened like the IBr^ 



The 10 arms are 70 mm. long. The first two brachials have a carination similar 

 to that on the IBr series but very much slighter. The first brachials are internally 

 contiguous in pairs, externally broader (longer), as are also the second brachials. The 

 proximal brachials are rounded and smooth. The first 10 brachials are discoidal, 

 those following irregularly oblique. From the fifteenth onward there is a low median 

 longitudinal crest slightly projecting in lateral profile. 



Syzygies occur between brachials 3 + 4, 13 + 14, 18+19, and distally at intervals 

 of about 5 oblique muscular articulations. 



PI is 5 mm. long with 13 segments. P a is also 5 mm. long with 13 segments. Pj 

 is 3.5 mm. long with 8 or 9 segments. P 8 is similar. PI is coarser than P 2 . The seg- 

 ments of these pinnules are rather uniform, smooth, a little longer than broad, distally 

 somewhat angular. P 4 to P J2 are 34 mm. long with about 10 segments of which the 

 proximal are very slightly flattened clorsoventrally. The distal pinnules arc 5-6 mm. 



