96 ART. 2. — H. MATSÜMOTO. 



friitectosus Lyman has !no peristomial plates, but the oral plates 

 and frames are of an elegant shape and cnrionsly twisted ; the 

 genital plates are thin, wide, long, and curved over the dorsal side 

 of the arm base ; no genital scales ; the basal vertebra?, have 

 large and thin wings without marginal grooves, and the vertebral 

 articulation is very peculiar with a large articular umbo and ne 

 articular peg. 



Certain species of Ophiacantha appear to stand at the very 

 base of the second type, which is found in those forms with the 

 arms more or less capable of coiling vertically. In Ophiacantha 

 bidentata (Linne), the peristomial plates are very large, simple, 

 rather thick, the oral plates and frames are more or less stout,. 

 the vertebrae are comparatively stout, and the vertebral articulation 

 is perfectly streptospondyline, the articular peg being absent. On 

 the contrary, Ophiacantha cuspidata Lyman is stated by the author 

 to have the zygospondyline vertebral articulation, with a well 

 formed articular peg. In Ophiolebes tuherosa Matsumoto, the peri- 

 stomial plates are very large, wide, thick, firmly fixed to the oral 

 frames, which are also very stout, and bear each two small 

 supplementary plates on the outer border. The vertebrae are short 

 and stout, with decidedly thick wings. The vertebral articulation 

 is of course streptospondyline. The genital plates and scales are 

 pecuharly undulated. The radial shields are narrow and bar-like. 

 The internal structures of Ophiosemnotes œdidisca (Claek) much 

 resemble those of the preceding, save that the radial shields are 

 wide, rounded and joined in pairs in internal view. According to 

 Lyman, Ophiocajnax hystrix Lyman has very stout oral plates and 

 frames, to which the peristomial plates are perfectly soldered, very 

 stout and short vertebra? with very thick wings and a perfectly 

 streptospondyline vertebral articulation. The vertebrae of Ophio- 



