MONOGEAPH or JvlPANESE OPHIÜEOIDEA. 153 



tive glands are covered by a sac-like membrane, which contains 

 very fine and delicate scales when viewed under the microscope. 



Key to Japanese genera of Ox)lnactinmœ, 



A — Oral angles not exceedingly short ; oral papillaB arising from the 

 oral plate ; dorsal arm plates entire, without supplementary ones . . 



Oiihiadis, 



AA — Oral angles exceedingly short ; oral papillœ arising from the adorai 

 sliield ; dorsal arm plates hemmed by a row of supplementary ones 

 along the outer, and often also lateral, sides OpJiiopJioIis. 



Key to Japanese species of Ophiactis, 



A — Three arm spines ; disk nearly or entirely free of spines. 



a— Fire arms; oral shields much wider than long hrachygenys. 



aa — Six arms ; reproducing by schizogony ; oral shields about as wide 



as long. 

 b- — Eadial shields separated from each other by a row of three scales ; 



uppermost arm spine the longest pteropoma. 



hh — Kadial sliields separated from each other by a single wedge-shaped 



scale, except at the outer ends, where they are in contact; middle 



arm spine the longest dyscrita. 



AA — Four or more arm spines ; disk beset with a number of spines. 

 c — Four arm spines. 

 d — Five arms ; disk scales fine ; radial shields sej^arated from each 



other by a row of four scales offinis. 



dd — Six arms ; disk scales coarse ; radial shields partially joined in 



pairs macrolepidota, 



cc — Five or more arm spines ; six arms ; reproducing by schizogony. 

 € — Five arm spines in free basal arm joints ; dorsal arm plates 



exceedingly wide, about thrice as wide as long; single oral papilla 



on either side modesta. 



