OPHITJRANS OF THE PHILIPPINE AND ADJACENT WATERS. 219 



species which I am describing below under the name of 0. cumulata, 

 in which the dorsal spines are sometimes thickened. 



In my description of 1904 I did not mention that the upper arm 

 plates may show on their distal border a row of extremely fine spines, 

 which, however, are not constant, but which I usually find on the 

 specimens collected by the Albatross; perhaps these spines did not 

 occur on the Siboga specimens. They appear to be, however, more 

 developed in the younger individuals, and they occur only for a 

 certain distance beyond the arm bases. Thus on the smallest of the 

 Albatross specimens these spines are very evident (pi. 52, fig. 4) and 

 on one of the arms they even occur beginning with the third seg- 

 ment, where they are two or three in number, becoming more numer- 

 ous and more obvious in the distal half of the arms; their number 

 and their size varies, however, with the individual, and as a rule 

 they only appear on the segments the arm spines of which are not 

 thickened. 



The thickening of the arm spines appears certainly to depend on 

 the age of the individuals, as I wrote in 1904; however, this thick- 

 ening does not appear to be exactly proportionate to the size of the 

 specimens. In all those collected by the Albatross the dorsal spines 

 are strongly thickened and shortened in the proximal portion of the 

 arms; the thickening occurs on the last dorsal spine and sometimes 

 also on that preceding the last, where it is, however, a little less 

 accentuated. The degree of thickening varies somewhat and it is 

 not entirely proportional to the size of the specimen. This thicken- 

 ing is very marked in the largest individuals in which the disk 

 reaches 7.5 mm. in diameter (pi. 49, figs. 4, 5), but it is equally 

 marked in a smaller specimen in which the disk is only 5.5 mm. in 

 diameter (fig. 6). It is slightly accentuated in a specimen in which 

 the diameter of the disk is 5 mm., while in another in which this 

 diameter reaches only 4.5 mm. it is more marked (pi. 49, fig. 3; pi. 

 52, fig. 5.). A single specimen, in which the disk is 4 mm. only in 

 diameter (fig. 2), has the dorsal spines scarcely modified; however 

 the indication of a tendency toward thickening may be noticed. 



On plate 98 as figure 2c I give some photographs of the club spines 

 of the dorsal surface of the disk, which are always very short ; they 

 are cylindrical, almost as high as broad, and carry on their outer 

 surface short and conical subequal spinules. The hook which repre- 

 sents the first ventral arm spine, while agreeing with the type most 

 frequent in the genus Ophiothrix, is remarkable for the great de- 

 velopment of the terminal branch, while the two others remain very 

 short and very narrow (fig. 25). The tentacle scale is stout and 

 rounded, provided on its free border with a few short, conical, and 

 unequal points (a). 



