MONOGEAPH OF JAPANESE OPHIUROIDEA. 327 



plates and scales are long and slender, being longer and more slender 

 than in the Ophiodermatidœ. The radial shield and genital plate of 

 the same side of a radius articulate with each other by means of 

 two articular condyles and one articular pit. The dorsal surface of 

 the vertebrae is rhomboidal and slightly notched at the inner end but 

 not so strongly as to be V-shaped. In Ophioplax lamellosa Matsumoto, 

 the peristomial plates are also triple, being however relatively shorter 

 and wider than in the preceding species ; the unpaired secondary 

 plate is very small and is slightly notched on the outside. The 

 oral frames are short and much more flared than in the preceding, 

 while the I'oof of the first oral tentacle pore is less projected 

 adradially. In other respects it is almost similar to the preceding. 

 In the Ophîonereidinœ, the internal structures approach those 

 of the next family, Ophiocomidœ, in certain points. In Ophionereis 

 annulata (Le Conte) and 0. reticulata Lütken, the peristomial plates 

 are double, without the unpaired secondary plate, and mucli smaller 

 than in the Ophiochilonince. The oral frames are very long, stout, with 

 well developed lateral wings for the attachment of very voluminous 

 chewing muscles. The teeth are very stout, quadrangular, with 

 widened and trimcated end. The dorsal surface of the vertebra3 is 

 strongly notched at the inner end corresponding to the elongated 

 outer end of the preceding vertebra, so as to be markedly V- 

 shaped. The radial shields, genital plates and scales are fundamen- 

 tally similar to those of Ophiochiton fasfigatus, though the radial 

 shields are much smaller. The internal structures of Ophiocrasis 

 marktannerl Matsumoto are similar to those of Ophionereis, except the 

 peristomial plates, which are triple, with a small unpaired secondary 

 plate. Now we come to a most interesting genus, OphiodoriSy 

 which is fairly intermediate in its internal structures between 

 Ophiochitonince and the Ophionereis- Ophiocrasis-iy^e. In OpJiiodoris 



