OPHIUKANS OF THE PHILIPPINE AND ADJACENT WATERS. 315 



63, fig. 6) for comparison with a similar view of the same structures 

 in 0. scolopendrina (fig. 5), and it may be seen that the differences 

 are very striking. The peristomial plates of 0. scolopendrina are 

 very thin, elongated, and four times as along as broad, while in O. 

 nigra these plates are very much more developed and broadened; 

 they are twice as long as broad only, with the borders slightly re- 

 curved. Viewed externally the mouth pieces of 0. nigra show an- 

 other peculiarity. The mouth shields are very much broader than 

 long, contrary to what is found in the genus Ophiocoma, in which 

 they are ordinarily elongated and longer than broad, rarely as long 

 as broad, and they are only broader than long quite exceptionally in 

 the single form from the island of Rodriguez which Smith has de- 

 scribed under the name of 0. brevispina. The adoral plates are very 

 elongated, and they extend for the whole length of the proximal 

 border of the mouth shield as far as the median interradial line where 

 they are in contact ; they thus come to be three or four times as long 

 as broad; these plates are very tapering in their internal portion 

 which runs along the proximal border of the mouth shield, while they 

 broaden outwardly to form a much developed lobe separating the 

 mouth shield from the first side arm plate. This form of the adoral 

 plate contrasts with that which occurs in the genus Ophiocoma in 

 which they remain always localized on the sides of the mouth shield, 

 showing a triangular shape and rather reduced dimensions; I have 

 recorded above the single exception known in 0. canaliculata. The 

 oral plates of 0. nigra are high and elongated, two or three times as 

 high as broad, while in the genus Ophiocoma they usually are very 

 low. 



These characters may be appreciated on the photographs which I 

 give here of different specimens of O. nigra, some from the northern 

 seas or from Roscoff, the others from the Azores and from Sicily (pi. 

 75, figs. 1-6). 



In the catalogue of recent ophiurans which H. L. Clark has just 

 published 0. nigra is given in the genus Ophiacantha under the name 

 of 0. sphaerulata (Pennant). This generic treatment, which is cer- 

 tainly based on the similarity in the characters of the spines, does not 

 seem to me acceptable for, among other things, the peristomial plates 

 of O. nigra differ entirely from those which we know in the genus 

 Ophiacantha, in which there occurs in each interradius a single large 

 and rounded peristomial plate, a condition which is entirely different 

 from that which my photograph shows (compare it with the figures 

 of Lyman '92, pi. 41, fig. 12, and also with that of Matsumoto '17 

 pi. 3, fig. 1). 



It therefore appears to me necessary to create for 0. nigra a new 

 genus, to which I propose to give the name Ophiocomina and which 

 is characterized as follows : 



