394 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



The cirri are almost the same in number, size, and number of segments as in the 

 larger pentacrinoid. But the radials are much less concealed and form a well-defined 

 cup. The articular facets do not occupy their whole sides, but a portion of the dorsal 

 surface remains on either side of each facet so that the width of the IBri is less than 

 that of the radials. 



Neither the axillaries nor the second brachials have such strong posterior proc- 

 esses as they do in the larger pentacrinoid, and the pinnules borne by the latter are 

 quite small with only 6 or 8 short segments. The pinnule on the fourth brachial is a 

 mere stump, and traces of still smaller stumps appear on some of the fifth brachials. 

 The following segments, up to the thirteenth, bear no pinnules, beyond this point there 

 are 6 or 8 pinnules on either side. 



Grieg (1904) has described in detail the pentacrinoid from Michael Sars station 

 74, 1902. This pentacrinoid, which is attached to a sprig of Bicellaria alderi, is 24 mm. 

 in total length, the crown being 7.5 mm. long. The uppermost columnals, just under 

 the centrodorsal, are short and discoidal, those in the middle of the stem are cylindrical, 

 and the distal are hour-glass shaped, being somewhat constricted centrally. The top- 

 most columnal is 0.18 mm. long, the second 0.14 mm., the third 0.23 mm., the fourth 

 0.37 mm., and the fifth 0.46 mm. The largest columnal is 0.64 mm. long, 0.28 mm. 

 broad at the ends, and 0.18 mm. broad in the middle. The centrodorsal bears a circlet 

 of 10 cirri which are 3 mm. long, composed of 9 to 10 segments and a terminal claw. 

 On the distalmost segment there is a feebly developed opposing spine, and on the distal 

 ends of the other segments there are small dorsal spines. The radials and brachials 

 recall most nearly those of the smaller Varna specimen, especially the axillaries. But 

 in the Varna specimen there are no pinnules on the 1 1 lowest brachials, while in this 

 there are pinnules on the second brachials. P! and P 2 are of equal size and have 

 about 15 segments, their form recalling that of the same pinnules in the adults. The 

 arms consist of 26 to 28 brachials. 



Grieg (1904) suggests that one of the pentacrinoids described by M. Sars (1868, 

 p. 50, pi. 6, fig. 20) which was dredged at Brettesnaes, Lofoten Islands, in 183 to 366 

 meters, belongs in reality to this species and not to Ilathrometra sarsi as supposed by 

 Sars. He bases his conclusions on the shape of the ambulacral deposits. But until 

 these are much better understood than they are now, and in view of the fact that 

 Heliometra glacialis is not known from the vicinity of the Lofoten Islands, it seems 

 safe to assume that Sars' determination was correct. 



History. The history of this species falls naturally into two divisions, which are 

 rather sharply separated. The first division includes the accumulation of information 

 regarding its range and habitat and the physical conditions under which it lives, and 

 is inextricably intertwined with the history of Arctic exploration, while the second in- 

 cludes the development of our knowledge concerning its anatomy and the finer details 

 of its structure and its development, and is quite inseparable from the history of the 

 same features in Antedon. The only one who has contributed to both lines of investi- 

 gation has been P. H. Carpenter. 



It is most practicable, however, to divide the history into a section outlining the 

 various expeditions by which this species has been obtained, which will serve equally 

 for all the other arctic crinoids, and a second section dealing with the records by indi- 

 viduals personally interested in this animal and including the anatomical, morpholog- 

 ical and nomenclatorial history. 



