12 ABT. 2. — H. MATSUMOTO : 



In both species, the upper and lower mnscular fossœ are both 

 large, a characteristic of the " common oploim-ans " in contrast to 

 the next two famihes, to which the Ophiohyrslnœ rather approach 

 in almost all characters. 



Key to Japanese genera of Ophiomyxinœ, 



A — Second oral tentacle pores opening outside the oral slits. 

 a — Disk free of spines ; radial shields absent ; arm spines not very 



consjpicuonsly thorny ; a few oral and dental papillae present ; no 



teeth. 

 h — Dorsal arm plates entirely absent ; arm spines connected together 



by a web-like membrane OpMosyzygus. 



hb — Rudimentary dorsal arm x^l^tes present, entire and hyaline ; arm 



spines free from each other OpMoleptoplax. 



aa — Disk beset with a number of long, acute, conspicuous spines ; radial 



shields conspicuous, each bearing one long, acute, conspicuous spine ; 



arm spines very cons]3icuously thorny ; a few spiniform oral papillae, 



besides one short and rounded outermost one, which arises from the 



fii'st ventral arm plate OpMostyracium. 



AA — Second oral tentacle pores opening within the oral slits. 



c — Teeth and oral papillge triangular, acute, not hyaline ; radial shields 



very rudimentary ; marginal disk scales present ; dorsal arm plates 



entirely absent ; arm spines converted into compound hooks 



Ophiostiba. 



cc — Teeth and oral papillae flattened, with widened and serrate end 



more or less hyaline. 

 d — Marginal disk scales present. 

 e — Rudimentary dorsal arm plates always entire ; radial shields very 



rudimentaiy ; vertebrae divided into halves, except in several basal 



arm joints ; arm spines converted into compound hooks . . Ophiohyalus. 

 ee — Rudimentary dorsal arm plates divided into several secondary plates, 



except in the distal arm joints ; radial shields not very rudimentary ; 



