OPHIUKANS OF UNITED STATES NATIONAL MUSEUM. 109 



The upper face of the disk is covered with very distinct plates whicli are of 

 middle size, pretty unequal, and imbricated; they display on their free margin an 

 extremely narrow fringe. Each plate is provided with a spine which is rather 

 strong and thick, but variably long and has always a very rough surface. Some- 

 times these spines arc elongated, presenting a certain number of strong, conicd, 

 and pointed teeth and having at their ends a few sharp spinules; sometimes, on the 

 contrary, they are short, although still terminated by some denticulations. The 

 interradial spaces are especially the place where the spines are most developed, 

 and the latter are particularly elongated at the margin of the disk, while in the 

 radial regions they are very short and may even be reduced to simple granules, 

 somewhat elongated and with a simply rough surface. The radial shields, clearly 

 distinct, and of middle size, are triangular mth their angles and margins rounded, 

 a little longer than wide, and separated on their whole length by one or two ranges 

 of plates; these shields show on their surfaces a few rounded or conical granules, 

 loosely and irregularly arranged, somewhat smaUor than the neighboring gi-anules. 

 Occasionally in a radius the two radial shields of the same pair are joined into a 

 single plate. 



The under face of the disk is provided with plates carrying spines identical 

 with those of the upper face and which extend as far as the mouth shields, but the 

 size of these spines decreases progressively until they are reduced to mere gi-anu- 

 lations in the vicinity of the said shields; their surface is still very rough but they 

 no longer offer such very distinct denticulations as on the upper face. The genital 

 slits are narrow and elongated. 



The mouth shields, of middUng size, are a little %vider than long, triangular, 

 with a rounded distal lobe, which protrudes more or less into the interradial space; 

 the proximal angle is obtuse, limited by straight sides which unite with the convex 

 distal edge by rounded angles. The adoral plates are rather smaU, with the prox- 

 imal edge slightly incurved; they are wader externally, but they do not separate 

 the mouth shield from the first brachial side plate. The oral plates are fau-ly 

 large, higher than -wide. The oral papillae amount to six or seven on each side; 

 the two external ones, widened and flattened, cover the tentacular mouth pore; 

 the others are thinner, elongated, and conical, with a blunt point. There is, 

 moreover, a certain number of tooth papillse which are not aU preserved in this 

 specimen, but the trace of which, at least, may be detected; some of them, amounting 

 to three or four, are a little larger than the oral papiUte and dnectcd horizontally; 

 the others, amounting to about the same number and arranged behind the former, 

 are smaller and directed obliquely downwards. 



The upper brachial plates are rather small and about as long as wide; they are 

 triangular or lozenge-shaped, according to the outUne of the distal edge which is 

 sometimes very strongly convex, sometimes plainly bent into two distinct sides 

 joined by a more or less blunt angle; the proximal angle is faii-ly open; the lateral 

 edges are divergent and join by very sharp angles on the distal side. These plates 

 are separated by a narrow interval. One can plainly distmguish, all along the 

 distal margin of the said plates, a set of very fme, sharp, and short little spines; 

 moreover, on closer examination, some similar but still shorter little spines will be 

 seen which are irregularly scattered over all the upper face of the plate. The 



