MONOGRAPH OF JAPANESE OPHIUEOroEA. 377 



and the other, forming the Chllophiurlda, is characterised essen- 

 tially by the radial shield and genital plate articnlating with each 

 other by means of two condyles and one pit of either plate. 



Among the Gnathophiurida, the Ampliilepidldce are evidently 

 most archetypal, being closely allied to the Ophiacanthidce with 

 only horizontally flexible arms, in the very large peristomial plates, 

 in the not very stout oral frames without well developed lateral 

 wings, in the very long and slender oral plates, in the genital 

 plates being not fixed to, but free from, the basal vertebrae, and 

 in the often incompletely divided vertebrae. 



The Amphiuridœ and OphiotricJiidce are characterised by the 

 very small peristomial plates, by the very stout oral frames with 

 well developed lateral wings, by the stout oral and dental plates, 

 by the very stout, quadrangular teeth and by the genital plates 

 being firmly fixed to the basal vertebrae. Among them, the 

 Ophiactinlnce are evidently nearest to the Amphilcpididce, because 

 neither have paired infradental papillœ or dental papillae. 



In my opinion, the paired infradental papillae of the Amphiu- 

 rince and the dental papillae of the OphiotricJiidce were acquired as 

 supplementary organs for mastication after the teeth had become 

 quadrangular and very stout. The Ampliiurinœ might be looked 

 upon as ancestors of the Ophiotrichidce, if the paired infradental 

 papillae and dental papillae could be proved to be homologous. 

 But according to Clark,' ^ the paired infradental papillae are 

 genuine oral papillae, while the dental papillae are modifications 

 of the teeth. Hence it appears that the two kinds of papillae just 

 mentioned are merely analogous organs adapted to a similar 

 function. The Amphiurince and Ophiotrichidce are then parallel 



1) Growth-Changes in Brittle Stars. Publication No. 182 of the Carnegie Institution, 

 Washington, 1914. 



