PART 6 A MONOGRAPH OF THE EXISTING CRINOIDS 361 



is that a close study of the specimens shows in some cases that individual arms of a 

 single example belong to the quadrata type while other arms of the same one must with- 

 out any question be determined as glacialisl He is firmly convinced that, as Levinsen 

 said, no sharp line of demarcation can be drawn between them. 



Michailovskij in 1905 still recognized quadrata as a distinct species. He said that 

 although the most characteristic features, the relative length of P 2 and P 3 and the shape 

 of the brachials, are sometimes very pronounced in the young of glacialis, some of the 

 Yermak specimens are in this respect so very typical of quadrata that he prefers to 

 assign them to this species until he is able to study more extensive material. 



Kalischewskij in 1907 admitted quadrata as a variety of glacialis, and in my earlier 

 work I recognized the form as valid, as stated by Mortensen (1910, p. 250). 



Both Derjugin (1915) and Djakonov (1926) maintained quadrata as a separate 

 species but in 1933 the latter followed Gorbunow (1932 and 1933) in reducing quadrata 

 to a form or variety of glacialis. Gorbunow commented that the status of quadrata 

 was doubtful and it might prove to be only a growth stage of glacialis. 



In 1886, P. H. Carpenter described a new species, Antedon barentsi, of which 

 the characters were given by him as follows: Centrodorsal hemispherical and thickly 

 covered with cirri except at the dorsal pole; these do not reach 20 mm. in length, and 

 consist of from 20 to 25 or 30 segments of which the fourth and the eight or ten following 

 are longer than broad and overlap slightly on the dorsal side; the later ones are some- 

 what sharpened and carinate, but there is very little trace of an opposing spine on 

 the penultimate. The radials are concealed. The IBr : are short, even at the sides, 

 and only just visible in the middle line of the ray, as they are deeply incised to receive 

 the strong posterior projections of the rhombic axillaries which are about as long as 

 broad. The first brachials have long outer sides and short inner ones which are well 

 separated above the axillaries. The second brachials are irregularly quadrate, pro- 

 jecting backwards into the first, but not so much so as to conceal them in the median 

 line of the arm. The first syzj'gial pair is roughly oblong, and the next 6 brachials 

 are quadrate with pinnules on the shorter sides, the longer sides being marked by 

 posterior projections. The lower and middle brachials are triangular and about as 

 wide as long, but farther out the length exceeds the width and the quadrate form is 

 gradually assumed. The distal edges of the brachials are somewhat raised so that 

 the dorsal surface of the arm is rather uneven. P[ consists of some 30 segments and 

 reaches nearly 15 mm. in length; the dorsal edges of the wide lower segments are cut 

 away at the ends so as to be somewhat pointed while those of the following segments 

 are sharpened, and traces of this sharpening appear on the more elongated later seg- 

 ments so that the end of the pinnule has a slightly serrate appearance. P 2 is much 

 shorter than P,, only reaching 8 mm. in length, and consists of about 20 segments of 

 which the basal ones are larger than those of the preceding pinnules, while P 3 is still 

 shorter, though with larger basal segments. The next following pinnules consist of 

 longish segments, the lowest of which are very stout and the later slender. In the 

 outer parts of the arms the pinnules are very slender and delicate with 15 segments. 

 of which the 2 lowest are flattened and expanded and the remainder elongated. The 

 gonads are fusiform, but not very long, only occupying about half the length of the 

 pinnules which bear them. The 6 or 8 segments which support them have their outer 

 sides produced upwards, and the perisome enclosing the gonads is thickly covered 

 with very irregularly arranged calcareous plates. The plates arc not very well defined, 



