272 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



I am not aware that anyone has ever noticed an analogous bifur- 

 cation of the spines of the dorsal surface of the disk among the 

 ophiurans. I know, however, of another case which I met with very 

 recently in an Antarctic Ophiaccmtha collected by the Australian 

 Antarctic expedition, which is part of an important collection the 

 study of which has been intrusted to me; I shall have occasion to 

 come back to it presently. 



The hook formed by the first ventral arm spine at a little distance, 

 from the disk in O. stelligera is strong and thick; it usually shows 

 three branches, rarely four; the two first branches, which are sub- 

 equal, are always much thickened and much elongated (pi. 102, figs. 

 2c and d) . 



The tentacle scale is small and terminated by a strong point ; some- 

 times it is doubled (g). 



The coloration of the individuals, which is so often very constant 

 in the different species of Ophiothrix, is extremely variable in 0. 

 stelligera; sometimes the general coloration is very light, generally 

 of a pinkish gray ; sometimes it is darker, gray or yellowish gray, or 

 it may pass into red or even to a dark brick red. In the median dorsal 

 line of the arms there may be seen a light longitudinal band bordered 

 by two dark lines; sometimes these lines are thin and regular, and 

 sometimes they are broken up into successive darker spots which 

 appear toward the distal angle of the upper arm plates; sometimes 

 the two lines are quite discontinuous and are broken up into succes- 

 sive elongated spots which may be very irregularly arranged and 

 lacking on certain segments. The red or reddish specimens usually 

 show in the median dorsal line of the arms a succession of white 

 spots which are unequal and irregular, not forming a continuous line. 



Two specimens show a very peculiar color type, which recalls that 

 of O. elegans; they come from stations 5139 and 5142; both are of 

 very small size and the diameter of their disks is only 4 mm. The 

 first (pi. 56, fig. 6), which is of a general light grayish color, has the 

 dorsal surface of the disk covered with club spines which run over 

 a little onto the radial shields, and among which are a very few true 

 spines ; a very dark narrow blue line with very clear borders extends 

 along the median line of the arms to their tips. The other specimen 

 (pi. 56, fig. 5) has a darker general coloration; the club spines of the 

 dorsal surface of the disk cover in large part the radial shields of 

 which the outlines are scarcely evident, and there are in addition 

 some long and strong spines, which are rather numerous ; a dark line, 

 of a blackish violet, occurs also on the median dorsal line of the arms, 

 but that line does not pass beyond the first ten segments. In neither 

 of the two specimens is the dark line of the arms continued on the 

 disk, while in O. elegans it reaches almost the center of it. In all the 



