376 AET. 2. — H. MATSÜMOTO; 



character of the arm plates. The Palaeozoic ophiurans are usually 

 very large, one specimen of Palaeozoic Myophiuroida at hand being 

 about as large as a very large specimen of Ophiomyxa ßacclda, 

 and another as large as, or larger than, a very large specimen of 

 Ophiarachna incrassata ; while the Ophiacantliidce are usually very 

 small, and their arms so slender as to equal in thickness only the 

 very distal part of the arms of the Palaeozoic Myophiuroida. I 

 imagine that the very small size of the recent Ophiacantliidce is 

 intimately correlated to their embryonal characters. 



The Hemieuryalidce are, in my opinion, evidently a terminal 

 group of the line of speciahsation represented at the base by 

 Ophiolehes, Ophiosemnotes, Ophiochondrella, &c., which are character- 

 ised by the pronounced vertical coiling of the arms. Among 

 them, the Ophiochnodrinœ are very close to the Ophiolehes -gvow^ 

 and more archetypal than the Hemieuryalince. 



The interrelationships of the Lœmophiuridà may be shown as 

 follows. 



Hemieiiryalinse 



OpliiocliondriuBe 



I 



I 



Ophiacantliidse 



with more or less 

 vertically coiled arms. 



OpliinciLiitlnd80 



with only horizontally 



flexible arms. 



From the Lœmophiuridà upwards, there are, in my opinion, 

 two distinct lines of specialisation : one, forming the Gnathophiurida^ 

 is characterised essentially by the radial shield and genital plate 

 articulating with each other by means of one large, conspicuous 

 socket of the former and one large, ball-like condyle of the latter ; 



