MONOGRAPH OF JAPANESE Oi'HIUROIDEA. 378 



US of the Opliiohyrslnœ. Tlie Trlchasterince are, in my opinion, 

 nearer to the Aster onycJiince than the Aster oschemat'mce are to the 

 same, because the ventral arm plates of both the Asteronychinœ 

 and I'richasterince are rather well developed and in contact with 

 one another, entirely separating the lateral arm plates, while those 

 of the Asteroschematince are very much reduced in size and 

 separated from one another by the lateral arm plates, which meet 

 in the ventral median line. This view almost coincides with that 

 of MoRTENSEN, wlio has pointed out the affinity of Aster onyx 

 to Euryale. The Asteroschematince are evidently descended from the 

 simple-armed group of the Trlchasterince. 



Whether the Gorgonocephalidœ are descended from the 

 Ophiohyrsince or from the Aster onychince is rather hard to decide, 

 though it is very evident, that the Gorgonocephaliclce have no 

 direct relation to the Trlchasterince and Asteroschematince. The 

 minute hooks of the arm annuli stand in an intimate relation 

 with the arm spines, as may be clearly witnessed in the very 

 distal arm joints, where the arm spines are hook -shaped and the 

 upper ones are smaller and show a tendency to sliift their positions 

 alternately so as to form a double row. These upper arm spines 

 are evidently the rudiments of the arm annuli. As already 

 mentioned, the lateral arm plates are approximated dorsally in 

 embryonal stages ; and such a dorsal approximation occurs, in the 

 present case, in the arm spines. So I imagine that the arm 

 annuli are due to the persistence of an embryonal feature of the 

 arm spines. If this interpretation be right, then the arm annuli 

 of the Gorgonocephaliclce remind us of the arm, spines of such 

 genera as Ophiobrachion and Asteronyx. Though Opkiohrachion is 

 referred to the Ophiohyrsince of the Ophiomyxldce and Asteronyx 

 to the Aster onychince of the Trlchasterldce, the difference between 



