2 6 5 



central canal, making with the median ridge an angle of about 45, or about a right angle 

 with each other; just bevond these lateral ridges, entirely unconnected with the ridge about 

 the central canal, separated from the lateral ridges by a ligament space about the same in 

 shape and size as the two lateral ridges, are two more ridges, slightly broader than the 

 others ; each has a very narrow fan-shaped space bevond it; bevond these two ligament 

 spaces, the distal borders of which are approximately at right angles to the dorsoventral 

 axis of the joint face, are two large obsolete muscular fossae which are about as high as the 

 distance between their proximal border and the dorsal edge of the joint face ; these are rounded 

 triangular in shape; inwardly each rises somewhat, forming two parallel, very inconspicuous, 

 low well rounded ridges, which are interiorly separated by a shallow rounded groove which 

 becomes more accentuated just bevond the central canal, where it separates the inner ends of 

 the inner pair of ridges; the inner ends of the ligament spaces just beyond these ridges are 

 bounded by the ridges bordering the muscular fossae interiorly. There is a deep intermuscular 

 notch the sides of which make an anole of from 6o° to qo° with each other. The rido-es on 

 the syzygial faces are high, and consequently the ligament fibres are long, appearing in dorsal 

 view almost quite as long as those of the neighboring dorsal ligaments. 



All the pinnules are present; Pj is about 16 mm.; the first segment is slightly trapezoidal, 

 viewed from the side about half again as long as broad; the second is between two and one 

 half and three times as long as broad, 2.3 mm. long; the following segments are similar, but 

 proportionately somewhat longer; the pinnule is moderately stout, like the proximal pinnules 

 of the large species of Psathyrometra, and is somewhat compressed laterally; the first segment 

 increases somewhat in diameter distally, the second decreases slightly, and the third also 

 decreases slightly, more especially in the proximal half; from that point onware! the pinnule 

 tapers very gradually. P 3 is 15 mm. long with ten segments, and resembles Pj ; the fóurth 

 segment, which is the longest, -is about three and one half to four times as long as broad, 

 and the fifth is about the same; but the sixth and following are onlv about twice as long as 

 broad, or slightly less. Only the bases of the following pinnules are preserved ; they appear 

 to become gradually shorter and more slender, the second segment decreasing rapidly in length 

 and progressively decreasing more and more rapidly in diameter distally, on the pinnule of 

 the ninth brachial being not quite so long as its proximal width, and slightly trapezoidal, so 

 that the following segments of the pinnule must be very slender. 



In locking into the relationships of this curious comatulid one naturally turns first to 

 the family Pentametrocrinidae, in which family the genus Pentametrocrinus also has but five 

 arms with no IBr series, and has the first syzygy between the fourth and fifth brachials instead 

 of between the third and fourth as usual. 



But in the Pentametrocrinidae (1) the disk is large and stellate and extends far out 

 upon the arms, being nearly or quite black in colour; (2) the cirrus sockets are closely 

 crowded and irregularly arranged on a rounded conical or hemispherical centrodorsal ; (3) the 

 individual cirrus sockets have no fulcral ridges nor produced margins; (4) the radials are 

 almost or quite concealed by the centrodorsal; (5) the lower brachials are more or less oblong, 



SIBOGA-EXPEDITIK XI.II /•- 34 



