PART 5 



A MONOGRAPH OF THE EXISTING CRINOIDS 



471 



mm 



FIGURE 21. Peromctra robusta (A. H. Clark), 

 holotype: a, Laterodorsal view of calyx; 

 b, distal half of cirrus; c, PI, broken but 

 probably of about 13 segments. 



there is & transition segment about the ninth; the division series and first two bracbials 

 have well developed synarthrial tubercles and marked lateral flanges; P! is 6 mm. 

 long with about 12 elongate, distally flared and spinous, segments; P 2 and P 3 are pro- 

 gressively shorter; P ft is present. 



Description. The centrodorsal is conical with swollen sides and a flattened and 

 coarsely papillose dorsal pole, 2 mm. broad at the base and 1.5 mm. high. The cirrus 

 sockets are arranged in 15 crowded and somewhat indistinct columns of usually two 

 each, the sockets of one column alternating with those in the adjacent ones. 



The cirri are about XXX, 39-47, up to 20 mm. long, rather stout and with the 

 distal portion capable of being tightly coiled. The first segments are broader than 

 long, the length increasing to the eighth to tenth (usually the ninth), which is a transi- 

 tion segment twice as long as broad. The segments following slowly decrease in length 

 so that the outermost are twice as broad as long, or nearly so. The distal dorsal 

 edge of the transition segment is slightly prominent. This feature gradually increases 

 in extent distally, on the last eighteen segments developing into a high thin median 

 dorsal process with a broadly rounded crest arising from nearly or quite the entire 

 dorsal surface of the segments. The opposing spine is long conical, arising from most 

 or all of the dorsal surface of the penultimate segment, its length equal to about half 

 the width of that segment; it is directed slightly distally. The terminal claw is about 

 as long as the penultimate segment and is slender and moderately curved. The cirri 

 are dark in color with a dull surface as far as the middle or outer third of the transition 

 segment, beyond that point white with a highly polished surface. 



The radials are short, between eight and ten times as broad as long, with a slightly 

 concave distal edge, and are closely united laterally. In dorsal view at right angles 



