152 AHT. 2. — H. jNIATSUMOTO : 



vacUcoIa Matsumoto, Ophiocentrus vert'icillalus (Döderlein), &c., and 

 am strongly impressed by the uniformity of the internal structures 

 of this family. The oral fi'ames are especially stout, with very 

 well developed lateral wings for the attachment of voluminous 

 masticatory muscles ; those of Ophiactis pteropoma are less stout 

 than those of tlie repi'esentatives of the other genera. The oral 

 and dental plates are very stout and more or less X- shaped in 

 internal view. The peristomial phites are rather or very small 

 and usually entire, save in the representatives of Amphiura and 

 Ophiocentrus, in w^hich they are double or rarely triple ; they are 

 comparatively large in Opliiopholis aculeata, Amphioplus auclstrotus, 

 Amphiura Iwrecc, A. trachydisca and Ophiocentrus vertlcillatus, but 

 exceedingly small in Hemlpholis elongata, Ophlophragmus japonlcus 

 and Ampliiura vadicola. The genital plates are firmly fixed to the 

 basal vertebrae, save in Ampldacantlia dicidua, nov., in whicli they 

 are free from the basal vertebrae. This peculiarity of the species 

 just mentioned is probably due to the fact that, the single type 

 specimen is very small and young. The genital plates of Ophio- 

 centrus verticillatus are somewhat unusual in position, lying entirely 

 dorsal, but not lateral, to the basal vertebra\ As to the genital 

 scales and the articulation of the genital plate and radial shield, 

 the statement in tlie diagnosis of the present order holds true for 

 all the representatives of the genera thus far studied by myself. 

 The dorsal side of the vertebrae is usually entire, without any 

 conspicuous notch inwards ; and only in Ophiocentrus verticillatus 

 is it distinctly notched inwards and more or less Y-shaped, 

 rather reminding us of that of the next family. According to 

 MoRïENSEN, Ophlopus arcticus Ljungman has very rudimentary 

 genital bursae, which are represented merely by the creases between 

 the arm bases and the interbrachial ventral surfaces, and the genera- 



