MONOGRAPH OF JAPANESE OPHIÜEOIDEA. 43 



ever, contain fine granules in younger stages .... section Ophiocreas. 

 c — Arms one-tliird to one-fourth as wide as the disk diameter. 

 d — Arms thirteen to seventeen times as long as the disk diameter, 

 e — Skin of the disk and arms very thick ; arm spines not very slender ; 



no large depressions just outside the tentacle pores caudatum. 



ee — Skin of the disk and arms very thin ; arm spines long and very 

 slender; a large depression present just outside each tentacle pore. 



, japonicum. 



dd — Arms about eight times as long as the disk diameter; skin of the 

 disk and arms moderately thick ; arm spines short ; genital slits 



very short, situated near the interbrachial angle ahyssicola. 



cc — Arms about one-half as wide as the disk diameter, and nine to 

 twelve times as long as the same ; skin of the disk and arms thick, 

 covering the underlying parts very loosely ghdinosum. 



It is by no means easy to distinguish clearly the species of 

 Asteroschema, especially those of the section Ophiocreas, owing to 

 the fact that, this genus assumes different appearances according 

 to its developmental stages. The oral papillae are papilliform and 

 arranged in a single horizontal row in younger stages, but are con- 

 verted into flattened and pavement-like grains in larger specimens. 

 The generative glands extend into the arm bases as two pairs of 

 ribbon- shaped bodies only in the adult, the extent of the lobes 

 increasing with gi'owth. The parts of the arms containing the 

 generative glands are much widened and knotted, owing to the 

 appearance of a transverse row of secondary plates on either side 

 of each arm joint. In the section Ophiocreas, the younger speci- 

 mens are more granular, and the full-grown ones are almost 

 entirely naked. The ratio of the arm length to the disk diameter 

 increases with growth. In exceedingly young specimens of a cer- 

 tain species, only a single arm spine (the adradial one in the 

 larger specimens) is present for each tentacle pore. On the basis 



