372 ART. 2, — H. MATSCJMOTO : 



arm plates of the two sides more or less completely. These genera 

 strongly resemble the Ophiomyxince, especially Ophioscolex, save in 

 the presence of well developed dorsal arm plates. I look npon 

 them to be a most archetypal, though not embryonal, group of 

 the Ophiacanthidœ. I of course believe that the gap between 

 the Ophiomyxmcc and Ophiacanthidœ is rather not very important. 

 Thus, the phylogenetic origin of the recent ophiurans may be 

 shown somewhat as follows. 



Ophiacantliidsei 

 Ophiomysinse 



Palaeozoic Myophiuroida 



Now, I will trace the Ophiomyxince-lino further. The Ophio- 

 byr since are evidently a step more advanced from the Ophiomyxince 

 toward the Trichasteridœ and Gorgonocejjhalidce, having very com- 

 pact oral skeleton and more or less short, stout, rather discoidal 

 vertebras with streptospondyline articulation. The only essential 

 distinction of the Ophiohyrsince from the Trichasteridœ and Gor-. 

 gonocephalidce arises from the fact, that the vertebrae of the sub- 

 family in question are less discoidal and have less well developed 

 upper and better developed lower muscular fossae, as compared 

 with those of the two last mentioned families. 



Among the Trichasteridœ, the Aster onychince appear to me to 

 be most archetypal, because the disk is large, the arms are com- 

 paratively slender, the lower muscular fossae of the vertebrae are 

 relatively little reduced and the arm spines are numerous, instead 

 of being reduced to two in number, thus more or less reminding 



