MONOGRAPH OF JAPANESE OPHIUKOIDEA. 381 



is found in the Ophlocomidœ, in which the dorsal surface of the 

 vertebraß is not distinctly notched at the inner end and the dorsal 

 arm plates are entirely free of supplementary plates. Therefore, it 

 appears to me not very improbable that the Opliionereidince and 

 Ophiocomidce may finally merge into a common stock at the very 

 base. I have observed that very young specimens of a certain 

 species of Ophiocoma have a squamated disk, which is almost free 

 of granules, and arms which in ventral view remind us of those 

 of Ophioplax and Ophioneretdmœ. As already pointed out, the oral 

 papillae are liable to be reduced when the masticatory apparatus 

 is very w^ell developed. This tendency is also observable in the 

 Ophiopsilince {Opliiocomîdœ). Moreover, the Opiuopsilinœ appear 

 to me to be slightly more specialised than the Ophiocomhiœ, 

 because the radial shields are fairly bar-like, the outer ends of the 

 genital plates more or less approximated to each other at the 

 dorsal side of the arm base and the tentacle scales very peculiar 

 in shape. I imagine that the Ophiopsilinœ represent a last phase 

 of the Ophiocommœ. 



As suggested by Kœhler, Ophiochiton appears to me to re- 

 semble much such genera as Ophlozona and Ophiozonella of the 

 Ophiolepidinœ. This resemblance might be of a superficial nature, 

 if the difference of the arm spines being erect or appressed were 

 of primary importance. But this diifference is observable even in 

 the proximal and distal parts of a single arm in many genera. I 

 therefore agree with Clark, who looks upon the diiference of the 

 arm spines in question not to be of primary importance. Then, 

 the relation of Ophiochiton to Ophiozona, Ophiozonella, &c. cor- 

 responds to that of the Ophiarachnince to the Ophiodermatlnœ. 



Among the Ophiolepidinœ, Ophioceramis has a very well 

 developed masticatory apparatus. Thus, we see that the mastica- 



