PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 87 



figs. 117-119, p. 134; Vid. Medd. Nat. Foren. K0benhavn, vol. 83, 1927, pp. 46, 47 (synonym 

 of /. adrestine). — Tortonese, Natura, Milano, vol. 24, 1933, p. 165. 



Diagnostic features. — The first three pinnules on the outer and usually the first 

 two on the inner side of each arm are similar, elongate, longer than their successors, 

 moderately slender, evenly tapering, and somewhat stifTened so that in preserved 

 specimens they are usually (but not always) nearly straight. They have 13 to 20 

 segments. 



The arms are from 35 mm. to 55 mm. and the cirri from 10 nun. to 14 mm. in 

 length. 



Description. — The centrodorsal is low rounded conical with a small more or less 

 prominently papillose polar area. The cirrus sockets are arranged in from three to 

 four closely crowded, regularly alternating, rows of which the peripheral has four 

 sockets in each radial area; they have rather prominent rims. 



The cirri are XXXII-L, 10-19 (usually 15-18), up to 14 mm. long. The first 

 segment is very short, the second is about twice as broad as long, the thu-d is shghtly 

 longer than broad, and the following increase in length to the si.xth which, wdth those 

 succeeding, is about three times as long as broad. On the last six segments the length 

 gradually decreases so that the antepenultimate is only about a third again as long 

 as broad. The penultimate segment is smaller than the preceding, slightly longer 

 than broad, and bears a stout opposing spine rising from nearly the whole of the dorsal 

 surface to a height almost equal to its distal breadth. The terminal claw is stout 

 basally, rather stronglj^ curved, and as long as, or longer than, the penultimate seg- 

 ment. The cirri are rather strongly compressed laterallj' and are of practically the 

 same width throughout. The ventral profile of the longer segments is concave, the 

 depth of the concavity moving gradually toward the proximal end, but the profile 

 of the shorter outer segments Ijecomes straight or slightly convex; the dorsal profUe 

 of all the segments is almost or quite straight. 



The radials are concealed by the centrodorsal, or their distal angles are just \asible 

 interradially as narrow prostrate triangles. The IBri are very short and very deeply 

 incised by the posterior processes of the axillaries which in a view perpendicular to 

 the dorsoventral axis completely divide them; their anterior borders are slightlj- swollen; 

 their lateral borders are somewhat abruptlj' produced so that they are in contact 

 with their neighbors. The strongh' convex main portion of the IBri narrows anteriorly 

 and this lateral production fills the gap which otherwise would be left; its surface is 

 abruptly marked off from that of the main portion, and usually somewhat raised. 

 The IBr2 (a.xillaries) are broader than long, with all the sides very concave; beneath 

 the sharp lateral angles they are extended proximally by a production which meets 

 the similar production of the sides of the IBri and is in contact ^vith that of the adja- 

 cent axillaries. Thanks to these lateral extensions the elements of the IBr series 

 and the fu-st two brachials are in close lateral apposition. 



The 10 arms are from 35 to 55 mm. long. The fu-st brachials are from two to 

 three times as long exteriorly as interiorly, and verj- deeph^ incised in the median line; 

 their outer border is somewhat abruptly extended laterally, and the outer edge is 

 straight; the inner edge is in contact with that of the adjacent fii-st brachial for the 

 basal half or two-thirds, the two edges thence diverging at approximately a right 

 angle. The second brachials are irregularh' quadrate, about as long as broad, with 

 the two pro.ximal sides strongly concave and a posterior process deeply incising the 



