A MONOGRAPH OF THE EXISTING CRINOIDS 



579 



Figure 35.—Poliometra prolixa (Sladen): a, Paratype, B.M., 81.8.26.10- 

 12, centrodorsal; b, B.M., 1957.10.31.4, Spitzbergen, centrodorsal. 



are about as long as broad and tbe following very rapidly become elongated and ex- 

 cessively long and slender distally; tbe distal edges of tbe segments are evcted and 

 finely spinous, this feature becoming more prominent distally. 



Pa is from 3.5 to 6.5 mm. (usually 4 to 5.5 mm.) long, with 11 to 17 (usually 

 11 to 13) segments, of which the first three are about as long as broad and the following 

 increase in length, though never becoming so elongate as those of Pi; P2 is stiff er 

 than Pi and tapers less gradually. 



P3 is from 5 to 10 mm. (usually 6 to 7 mm.) long ^vith 11 to 15 segments and 

 resembles P2; P4 is 8 mm. long and resembles P3. 



The first inner pinnule, Pg, is 19 mm. long with 35 segments. 



The distal pinnules are 15 mm. long. 



Dr. Gislen has pointed out (1923) that there are two different types of am- 

 bulacral deposits in this species. Specimens from Greenland and the Faroe Channel 

 have the spicules rather slender and smooth (var. groenlandica) , while those from 

 Nova Zembla, the Kara Sea and Taimyr have coarse and extremely spiny spicules 

 (var. siberica). Specimens from Spitzbergen resemble those from Greenland in 

 having slender spicules which, however, are somewhat spiny. 



Dr. Th. Morteusen (1903) described the ambulacral deposits as long narrow 

 curved rods, shghtly broadened and with a few holes at the outer end; the proximal 

 part is bent parallel to the pinnule segments and is sometimes slightly irregular, or 

 even provided with a few holes. These deposits arc not developed in the integument 

 of the expanded portion of the genital pinnules. 



He also noticed that the segments of the middle pinnules are rather long and 

 slender. There is a thin keel on the inner side but the outermost 4 or 5 segments 

 are quite cylindrical and without a keel. The outer side of the segments is smooth, 

 and there is a circlet of spines about the distal end. 



Gislen found that specimens from western Greenland seem to have rather spiny 

 distal segments approacliing in appearance those of Haihrometra sarsi. 



