A MONOGRAPH OF THE EXISTING CRINOIDS 91 



In species of Comatella with 20 arms each IBr series bears 2 IIBr series, and each 

 of these IIBr series bears 2 arms. The 2 arms borne by each IIBr axillary are not 

 quite alike, for the outer arm has a syzygy between brachials 3+4, and sometimes 

 also between brachials 1+2, while the inner arm has the first syzygy between brachials 

 1+2, and none between brachials 3+4, the second syzygy being, as a rule, a con- 

 siderable distance beyond the first. 



In Comatella stelligera additional axillaries are typically developed only on the 

 outer side of each ray, so that the IIBr and succeeding axillaries bear an axillary on the 

 face sloping toward the outer side of the ray and an undivided arm on the inner face. 

 This gives the appearance of 2 stout arm trunks arising from the IBr axillary which 

 give off on the inner side undivided arms on alternate segments, finally ending in a 

 pair of arms. 



In the very large C. nigra each ray typically bears 4 instead of 2 such arm trunks, 

 2 arising from each IIBr a>dllary. 



The number of arms, at least in the larger species, is variable within rather wide 

 limits. Thus in C. nigra the arms may be as few as 27 or 29, or as many as 80 or more, 

 though in most individuals they number between 40 and 55. In C. stelligera the arms 

 may be as few as 12 or as many as 45 or even more, though there are usually between 

 30 and 40 arms. 



The number of arms is therefore not wholly rehable as a criterion for the differ- 

 entiation of the species, in which the most emphasis should be placed on the characters 

 furnished by the size of and number of segments in the cirri. 



Terminal combs are found on a variable number of the proximal pinnules, but 

 never beyond the sixth or seventh pair. Pi is of variable size, but is always much 

 longer than the succeeding pinnules, which decrease in length. 



The disk usually bears a greater or lesser nximber of conspicuous calcareous 

 granules, though it may be naked. The mouth is usually marginal and the anal tube 

 central, or nearly so; but in some individuals both mouth and anal tube are more or 

 less equally subcentral. 



In contrast to the variability in the division series of the multibrachiate species 

 in the other comasterid genera the uniformity of the division series in Comatella is 

 remarkable. Only two instances of deviation from the usual type have been recorded. 

 In a specimen of C. nigra one of the division series was doubled, consisting of 4 ossicles 

 in 2 synarthrial pairs, and in a specimen of C. decora Gisl^n found a IIBr 4 (3 + 4) 

 series followed by arms having a pinnule on the first brachial and a syzygy between 

 brachials 2 + 3 as in Capillaster. 



KEY TO TUE SPECIE3 IN THE GENUS COMATELLA 



a'. Cirrus segments usuaUy 26-30; arms usually more than 40; all the IIIBr series present, and 

 usually numerous IVBr, VBr, and VIBr series, and sometimes VIIBr series, also; the inner 

 branch from each IIBr series in its divisions resembles the outer (from the Philippine Islands 

 to Torres Straits, the Abrolhos Islands, Western Australia, and Sumatra; 0-106 meters). 



nigra, p. 92. 



