14 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



wide, but they do not extend much beyond the distal margin of the mouth shields. 

 The genital slits are narrow, but quite distinct, and they are continued nearly 

 up to the end of the mouth shields, on the same level as the middle of the first 

 lateral brachial plate. 



The mouth shields are large, elongated, but their width is not very important; 

 they are almost pyriform and much more widened distaUy than proximally; they 

 are almost twice longer than wide. They offer a very obtuse and short proximal 

 angle, and then, a Uttle further back, they are somewhat notched by the extremity 

 of the genital sUt; beyond that, they first grow rapidly mder, and then more slowly 

 so, up to their distal part which is limited by a strongly rounded border. The 

 adoral plates are fairly wide with their two margins almost parallel, but narrower 

 without than within; they are one and a half longer than wide. The oral plates 

 are pretty high. The oral papillae amount to sbc at least on each side, but the four 

 or five external papiUse, very low and rectangular, are more or less jointed and their 

 outUnes are hardly apparent; the innermost papilla is conical and pointed, and it is 

 smaller than the odd terminal papilla, which is also conical and pointed. All these 

 mouth plates, as well as those of the under face of the disk, are covered with fuie 

 rounded granulations. 



The arms, fairly broad at their bases, grow rapidly tliinner; they are hardly 

 carinated and their upper face is convex. Only the first upper brachial plate 

 is large, triangular, with a very obtuse proximal angle and a very convex distal 

 mart'in. The second one, of hexagonal shape, is extremely wide and at least twice 

 wider than long, with a concave proximal margin, and a very convex distal margin, 

 while the lateral margins are each resolved into two little sides meeting in an obtuse 

 angle. The third and fourth plates are still hexagonal, but their width rapidly 

 decreases at the same time as the proximal side becomes narrower, so that they 

 assume a triangular shape, with a proximal angle which is truncated on the fifth 

 and sixth plates, but their distal margin may generally be divided into two distinct 

 sides which meet in an obtuse angle; these plates remain wider than long and they 

 part, from the sLxth or seventh, upward. Beyond that the plates become tri- 

 angiilar, a little wider than long, with very sharp angles and a feebly convex distal 

 margin. The first plates are granulous, like those of the upper face of the disk, 

 but the granules very soon disappear and the surface of the former becomes almost 

 smooth, contrary to what happens with the neighboring lateral plates which always 

 remain more or less strongly granulated. 



The under bracliial plates are rather small and a great part of the under face 

 of the arms is covered by the lateral plates. The first four or five under brachial 

 plates are separated from one another by a narrow and shallow transverse furrow. 

 The first under plate is large, triangular, with the proximal angle truncated and 

 the three sides somewhat excavated. The second one, trapezoidal, is as wide as 

 the first one, but it is vnder than long, with the distal side longer than the proximal 

 one, which is excavated. The third plate is trapezoidal also and wider than long, 

 but narrower than the preceding one. The fourth plate, still trapezoidal, is a 

 little longer than wide and its distal margin is almost straight. The fifth and sLxth 

 plates are also a little longer than wide, but they become narrower than the fourth 

 and their proximal margin is apt to be elongated into a slightly obtuse angle. 



