^ 



106 



THE 0PIIIUT1TD7F.. 



naked. The arms are not wider outside the disk than on the part enclosed 

 in the disk; they are rather high, rounded, triangular in cross section. 



The central part of the disk is covered with a naked skin^ in which only 

 some few very small, widely spread plates are seen (in dried specimens). 

 Alon<^ the margin the disk is covered with small, irregular, but distinct 

 scales, which are also found along the margin of the radial shields. These 

 are rather large and conspicuous, almost as long as half the radius of the 



■ 



disk ; they are oval in outline, only the outer edge is almost straight. 

 Usually they are widely separated by several rows of scales, sometimes only 

 by one row of rathet large scales. No marginal plate in the interbrachial 

 space, and of course no primary plates. The whole under side of the disk 

 covered with very small overlapping scales. Sometimes there are a few 

 grains on the disk, especially round the radial shields. No genital scales 

 distinct, no papilla) along the large genital shts, which reach to the margin 



of the disk. 



Only two very short arm-spines, sometimes three, in the inner part of 

 the arm, and farther out only one ; the upper one is usually a little longer 

 than the other. They are not inserted on the outer edge of the side arm- 

 plates, but a little below, on a little elevation ; they only reach to the outer 

 edge of the side plate. The tentacle pores are large, and very conspicuous; 

 the first 4-5 pairs have two papilla) at the distal edge, one wide and flat, the 

 other short, rounded- Farther out there are two rather elongated, pointed 



r 



scales at the proximal edge of the pore, and these continue in the whole 

 length of the arm. 



Color in alcohol : gray, with a bluish tint. 



Several specimens from Stations 3360, 1672 fathoms; 3398, 1573 f . ; 

 3399, 1740 f. ; 3400, 1322 f. ; 3414, 2232 £ 



r 



This species is very variable as to the form of the plates, especially 

 mouth and side mouth shields; it is rare to see them so regular as in the 

 fvmre, which however must be regarded as the typical form. Often they 

 are broken or quite irregular in outline. This is no doubt due to the feeble 

 calcification. One specimen has two-three small papilla) at the outer edge 

 of the radial shields, as a rudimentary arm-comb. 



0. semimidiis is very closely related to 0. vallincola Lym., and perhaps it 

 is really the same species. Judging from the figures given by Lyman (Chal- 

 lenf^-cr, V., Plate XXIV. Figs. 16-18), they are not identical: the mouth 

 papilla), mouth shield, side mouth shields, first ventral plate, the inner dorsal 



t 



■ 



» 





