178 AliT. 2. — H. MATSÜMOTO : 



separated from each other. Four or five pairs of oral papilla3 to 

 each oral angle, short, close- set ; the apical infradental pair arise 

 from the dental plate, and the outermost pair from the adorai 

 shield. Arms long, slender, flattened, inserted ventrally to the 

 disk, only horizontally flexible. Three to six arm spines. One 

 or two small, leaf-like tentacle scales. 



This new genus includes Oplnostigma fonnosa Lutken, 1872, 

 Ophiocnida sexradia Duncan, 1889, Amph'iura notacantha Lutken & 

 MoETENSEN, 1899, A. gastracantha Lutken & Moktensen, 1899, 

 Ophiocnida libera Kœhler, 1907, 0, amphacantha McClendon, 1909, 

 Amphilimna pentacantha Clark, 1911, and Amphiacantha dividua, 

 noY., besides the genotype, Amphiopliis acanthinus Claek, 1911. 



Amphiacantha is practically Amphioplus with disk spines, and 

 differs fi^om Amphilimna Veeeill (non Claek, 1911), in the 

 divergent radial shields, in the close-set oral papilla^ in the not 

 very long, but short and flattened outermost oral papilla, in the 

 fewer arm spines, and in the not long and spiniform, but short 

 and leaf-like tentacle scales. 



Key to Japanese species of AnipJnacantha, 



A — Three arm spines ; two tentacle scales ; radial shields not very small, 



joined or closely set in pairs. 

 a — Disk spines very numerous, very short, l.iluut, present ou both tlie 

 dorsal and ventral sides ; radial shields joined in pairs ; oral shields 



mucli wider than long; ventral arm plates Lmger than wide 



formosa. 



aa — Disk spines not very numerous, very long, slender, acute, present 

 only on the dorsal side ; radial shields divergent, the pairs being 

 in contact only at the outer ends ; oral shields much longer than 

 wide ; ventral arm plates wider than long acanthiua. 



