A MONOGRAPH OF THE EXISTING CRINOIDS 95 



rather small, discoidal, with the dorsal pole slightly concave, 5 mm. in diameter; the 

 cirri are XVII, 25-26, about 30 mm. long; the specimen from station 53 is a fine 

 example with 27 arms 165 mm. in length; the IIIBr series are externally developed; 

 the cirri are XX, with some more or less developed in addition, 32-39, up to 37 mm. 

 in length, long and stout; the seventh or eighth is a transition segment; following 

 the transition segment the cirri become somewhat abruptly less stout. 



Of the specimens collected by Dr. Th. Mortensen off Jolo, one from about 18 

 meters has about 50 arms, and the one from about 36-55 meters is large and typical. 



Varietal specimens. The specimen from Albatross station 5356 is curious in 

 having only 29 arms, which are 170 mm. in length; the IIBr series bear a IIIBr series 

 externally and an undivided arm internally except in one case, where a IIBr series 

 bears merely 2 undivided arms. 



The specimen from Albatross station 5413 has 40 arms 170 mm. in length; the 

 cirri are XXI, 30-32, from 30 to 33 mm. in length. 



The example from off Long Island, Abrolhos, has 40 arms about 110 mm. long; 

 the "very powerful cirri" are XXII, 25-28; the disk is about 32 mm. in diameter. 



In the number of arms and in the arrangement of the arm divisions these speci- 

 mens resemble typical stelligera instead of typical nigra, but in the structure of the 

 cirri and pinnules and in all other points they agree with nigra. It would thus appear 

 that while the frequency of the arm divisions can usually be relied upon to separate 

 these two forms it is not so reliable as the characters presented by the centrodorsal 

 and the cirri. 



Abnormal specimen. In an example without locality in the British Museum one 

 of the division series is composed of 4 ossicles, of which the outer 2 are united by 

 synarthry. 



Anatomical notes. Dr. P. H. Carpenter found that this species is remarkable 

 for the great development of the branches of the axial cords of the arms and of the 

 parambulacral network which is connected with them in the ventral perisome, and 

 also for the large size of the radial blood spaces beneath the ambulacra. 



These large radial blood vessels may frequently be found to contain yellow 

 pigment masses or coagula. They are sometimes triangular in section with the apex 

 pointing downward so as to be received into a strongly marked concavity in the upper 

 edge of the water vessel. 



In nearly all the crinoids the epithelial lining of the genital tube is continuous 

 with that of the ovary. Individual cells of this lining enlarge at the expense of their 

 fellows and are gradually inclosed in follicles which are derived from the original 

 ovarian epithelium. These follicles project freely into the lumen of the gland, but 

 there is ordinarily practically nothing that could be called an ovarian stroma. In 

 this species, however, there is a highly organized stroma separating the follicles, 

 and young ova may be found in it at all stages of growth, the smallest being no 

 larger than the nucleolus of a mature ovum. But Carpenter was unable to make 

 out the derivation of these germs from the epithelial cells as clearly as may be seen 

 in Heliometra glacialis and similar forms. 



The lateral branches of the axial cords of the arms are especially well developed 

 in this species. 



