MONOGEAPH OF JAPANESE OPHIUEOIDEA. 23 



are smaller in the basal joints, and only one is present in tlie 

 first and second, but two in the third and fourth. No tentacle 

 scale. 



Colour in alcohol : disk bluish gray ; arms light yellow ; disk 

 and arms of younger specimens light grayish pink. 



In the smaller specimens, the disk skin is seen to contain, 

 when examined under a microscope, very fine scales scattered in 

 it, much resembling the perforated spicules of a holothurian ; but 

 in the larger ones they are entirely absent. The oral papilla?, the 

 papilla? just below the first oral tentacle pores, the teeth and the 

 arm spines appear to increase in number witli the growth of the 

 animal. In tlie specimens before me, the arm spines are not so 

 long and so slender as are shown in Claek's figure. Further, his 

 figure appears to me to be inaccurate in so far as it represents 

 the arm spines as being two in number and equally long already 

 in the first arm joint. 



Ophiohynien gymnodisciis Clark. 



OpMoJiymen gijmnodiscus : ClaPlK, Bull. U. S. Nat. Mns., LXXV, 1911, 

 p. 277, fig. 140. 



Eastern Sea ; 107-139 fathoms (Clark). 



Key to Japanese genera of OpMohyrsinœ, 



A — Radial shields more or less long and bar-like ; disk or, at least, 

 radial shields spinulate ; arm spines spiniform, not all converted 

 into compound hooks. 

 a — Dorsal arm plates entirely absent ; arm spines very long and 



serrate. , OpMophrixus. 



aa — Rudimentary dorsal arm plates present, being divided into a num- 

 ber of secondary plates ; arm spines rather short and not serrate. . . 

 Ophiobyrsa. 



