98 AET. 2. — H. MATSUMOTO. 



lih — Disk scales visible, sparsely beset with gi-anules, spines or stumpy 



tubercles ; oral shields usually joined with the first lateral arm 



plates ; oral angles free of granules. 

 i — Arms strongly knotted, with very prominent spine ridges ; arm 



spines of both sides of free basal joints approximating dorsally; 



dorsal arm plates very small, widely separated from each other by 



the lateral arm plates OpMomit relia. 



il- — Arms not very knotted ; arm spines of both sides not approximating 



dorsally ; dorsal arm plates not very small, in contact with each 



other at least in proximal arm joints. 

 / — Basal tentacle pores not especially large ; single flat tentacle scale 



to each pore ; radial shields oval OpMopJdhalmus. 



jj — Several first tentacle pores especially large, while the outer ones are 



very small ; no true tentacle scales, Avhicli are represented by a 



number of lowest arm spines much smaller than the upper ones. . . 



Opldentrema. 



gg — Radial shields long, narrow, bar-like. 

 k — Radial shields separated from each other; disk, as well as radial 



shields, more or less closely covered with granules, spines or stumpy 



tubercles Opliiacantha. 



JcJc — Radial shields perfectly joined in pairs, naked ; disk sparsely beset 



with spines or granules, the disk scales being quite distinct 



Ophiacanthella. 



ß'- — Radial shields large, long and wide ; disk scales quite distinct. 



I — Oral j)apilla3 arranged in a regular series. 

 m — Outermost oral papillœ large and operculiform ; arms strongly 



knotted, with veiy prominent spine ridges ; arm spines of both sides 

 of free basal joints approximating dorsally ; dorsal arm plates very 



small, widely separated from each other by the lateral arm plates. 

 -n — Disk distinctly five-lobed ; radial shields divergent, those of a pair 



slightly in contact in the outer parts ; oral shields small, separated 



from the first lateral arm plates by the adorai shields ; interbrachial 



ventral surfaces covered with numerous fine scales ; genital bursaa 



