292 ART. 2. — H, MATSUMOTO : 



Ophiopenia discicantha Clark. 



OpJdopenia disacantha : Clark, Bull. U.S. Nat. Mus,, LXXY, 1911, 

 p. 102, fig. 38. 



Sea of Japan ; 176-200 fathoms (Claek). 

 Bering Sea. Alaska. 



Revision of Ophiozona. 



I have great doubt about the generic value of Oplnozona as 

 now understood. The genotype, Ophiolepis impi'essa Lütken, 1859, 

 has very numerous small disk plates surrounded by a zone of 

 much finer scales, and well developed, quadrangular dorsal, as 

 well as ventral, arm plates, which are perfectly joined to one an- 

 other. A characteristic feature is the presence of a group of three 

 disk plates between the outer parts of each pair of radial shields. 

 In every character, the genotype is very nearly allied to the genuine 

 Ophiolepis and distinguished from it merely by the absence of 

 supplementary dorsal arm plates. But most species of Ophmicma 

 as understood at present, differ much from the genotype, having 

 less numerous large disk plates and less well developed, rhomboidal 

 dorsal, as well as ventral, arm plates, which are separated from 

 one another outside the arm base by the lateral arm plates. 

 Moreover, the trio of disk plates above mentioned is entirely 

 absent. Another atypical group of Ophiozona is represented by 0. 

 gymnopora Claek, 1909, which is characterised by the disk being 

 elevated high above the arm bases, by the completely joined 

 radial shields, by the granulated interbrachial ventral surfaces, by 

 the indistinct genital slits, by the first ventral arm plate being 

 larger than the following, by the second oral tentacle pore opening 

 entirely outside the oral slit, and by the total absence of the 



