324 1- IJIMA AND S. IKEDA. 



Hoyle'^ seems to have entertained some rlouht as to whether 

 O/nMlioteutlu's, together with Slauroteutlris Ver., is not identical with 

 ('irrofeittltis of Eschricht. In our judgment, so far as Opistlioteiiihis is 

 concerned, its generic distinction may wel] be considered as valid, 

 preeminently on account of the unusually depressed head and body, 

 which condition, conjointly with the tliick and swollen briichial webs, 

 gives to the animal a shape quite exceptional among Cephalopods. 

 Except for the projecting tips of its arms, it may be compared to a 

 plnno-convex disc, of which the plane side is the inferior or the 

 anterior and re[)resents the innei' surface of the umbi-ella. The arched 

 suj)erior or posterrior surface includes not onl}^ tlie posterior aspect of 

 an ordinary ceplialopod body, but also the dorsal and ventral surfaces 

 as well as the outer surface of the uinbrella. The head and body are 

 thus flattened aritero-posteriorly. This is accompanied, as might 

 naturally occur, by a,n outspread of these parts laterally and especially 

 along the ventral web, whereby such parts are, so to say, pushed 

 into the umbrella beneath its outei- skin. Hence, the lateral portions 

 of the broadened head and body lie directly over the bases of the 

 lateral arms, while the median porti(Hi of the body directly overlies 

 the two ventral arms to a considerable extent. At the same time the 

 siplion and the branchial apertiu-e are shifted over to a, considerable 

 distance on the outer surf ire of the median ventral web, and are 

 directed in the ventral, not in anterior direction as is usually the 

 case. The close and wide (-(^nnection thus established between the 

 head and body on the one hand and the umbrella on the other, 

 accounts for the fact that the latter, with arms enclosed in it, is 

 horizontally expanded, the former acting as a restraint against its 

 closi ng. 



1) Challenger Report. Vol. XVI. p. 230. 



