100 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



region and wider again outwardly, where they build a blade which, besides, is very 

 thin and which separates the mouth shield from the first lateral brachial plate. 

 The oral plates arc very high and narrow, and do not exceed the middle of the adoral 

 plates. The oral plates bear on their free edge a sometimes rather irregular row of 

 oral papillse which most generally amount to seven; these papillae are conical, 

 elongated and rather narrow, with an obtuse end; sometimes there are one or two 

 supplementary papillse inten^alated among the normal ones, breaking the arrange- 

 ment of the latter. The two external papillae scarcely differ from their neighbors; 

 they are, however, a little shorter and also slightly more widened and more obtuse, 

 but they can hardly be said to offer a peculiar differentiation. This row of oral 

 papillfe suddenly stops outwardly, and it scarcely reaches the third part or the 

 middle of the tentacular mouth pore which remains absolutely unarmed around 

 its entire outline. In none of the specimens do I observe the slightest indication of 

 papillae, either on the external or the internal side of tliis pore, neither do I observe 

 it on the under face of the oral plate. At the extremity of the jaws, there appear 

 sometimes two and sometimes three large tooth papillae. 



The shape of the upper brachial plates suggests that of Opiiiopristis ensifera. 

 These plates are, however, comparatively a little wider than in the latter species, 

 and, besides, their shape is plainly triangular and not lozengelike; they offer, over 

 their whole length, a slight median crest. The very obtuse proximal angle is 

 limited by two slightly convex sides; the convex distal side offers, in its middle, a 

 small lobe which corresponds to the median keel; the lateral angles are very sharp. 

 On the first brachial articles, the median protuberance of the distal side is more 

 conspicuous, and this side itself may be resolved into two sides which meet by a 

 protruding and very obtuse angle. These plates are almost twice wider than long 

 and they are all contiguous. 



The first brachial under plate is fairly small, trapezoidal, M'ith a proximal side 

 which is larger than the distal side; these two sides are slightly convex and the 

 lateral sides are diverging. The following plates are pentagonal with a very obtuse 

 proximal angle, divci^ing lateral sides which are very widely excavated by the cor- 

 responcUng tentacular scales, and a very wide and strongly convex distal side. In 

 the largest spe<;hnens the first two or three plates have their proximal angle opened 

 to such an extent that it almost reaches lcSO° and the outline then becomes simply 

 rectangular. These under brachial plates are, first, much -wider than long, then 

 they become narrower and just as wide as long, and finally they are longer than 

 wide; they always remain contiguous. The middle of each plate is slightly pro- 

 truding, chiefly near the proximal angle. On the surface of these plates and mainly 

 at a certain distance from the disk, one can see a mark consisting of two lines which, 

 starting from each antero-lateral angle, meet at an acute angle at a certain distance 

 in front of the distal side. This mark is not nearly so plain at the beginning of the 

 arms, where, besides, the two lines form a less acute angle; it is analogous to that 

 which Lyman has indicated in Ophiacantha placentigera, a species which Yerrill 

 also has classified in his genus Ophwtrda, but here it extends over a greater length 

 of the plate. 



The lateral plates have on their distal side, which is fairly protruding and 

 thickened, five flattened, transparent spines which are provided on their edges 



