I 



128 



THE OPIIIURIDil^]. 



end; it thus consists of one small median and two large lateral pieces. 

 (Plate IV. Fig. 10.) Other specimens have the mouth shield divided into 

 two pieces only by a median line. (Plate V. Fig. 1.) Side mouth shields 

 rather short and broad^ meeting within. The whole mouth angle is some- 

 what hollowed. 



First ventral plate with inner edge rounded, outer edge forming a very 



obtuse angle. The other ventral plates triangular, with the sides a little 

 curved ; the second to fourth have their lateral sides inconsiderably re- 

 stricted by the tentacle pores. They are equally long and broad, all widely 

 separated. The side arm-plates have the outer edge a Httle prominent ; 

 they meet above from the fourth or fifth joint. The dorsal plates are 

 divided in two pieces by a longitudinal line, which is rather irregular; 

 sometimes it is almost straight, median ; sometimes it is wholly wanting 

 on a few joints, the dorsal plates there being thus undivided. They are 

 triangular, the first three or four, which are in mutual contact, with inner 

 end truncated ; outer edge rounded ; they are equally long and broad. 



The disk is covered with rather coarse, not overlapping scales, among 





which the primary plates are distinct; round the scales there are some 

 indistinct ridges. The radial shields not very large, somewhat irregular, 



r 



separated by a single row of scales, sometimes just meeting without. 

 Incisures of the disk at the base of the arms very inconsiderable, enclosing 

 one rudimentary dorsal plate; interbrachial spaces with a distinct marginal 

 plate. The ventral side of the disk almost wholly covered by a large plate 

 outside the mouth shield, sometimes divided by a median line (Plate V. Fig. 1), 

 and by the large genital plates; only a few small scales are seen along the 

 margin. The edge of the disk not sharp, both sides being rounded towards 

 the margin. Papillae along the genital slits close set, square, rather indis- 

 tinct; arm-comb little developed, only four papillse to be seen from above ; 

 they are small and rounded. The genital scales sometimes do not reach the 

 dorsal side of the arm, the papilla) then are inserted on the outer edge of 

 the radial shields. No secondary arm-comb. 



Four short arm-spines, three close together below, of which the middle 

 one is the longest, and one being apart at the upper side of the arm. Only 

 four tentacle pores, very small, except the first, which does not open into 

 the mouth space. Tentacle scales ; first pore three on outer, two on inner 

 side; second and third, two on outer, one on inner side; fourth, two on 

 outer, none on inner side. 



^ 



1 



ff" 



