60 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



separated by several rows of small plates from the primary radial ones, which are 

 smaller than the former. The plates grow larger toward the radial shields, as 

 well without as within these shields, and they separate the two shields of each 

 pair by several rows. The radial shields are elongated, with a straight radial side 

 and a convex interradial side; they offer a narrow distal side and a rather sharp 

 proximal angle. Their length is inferior to half the radius of the disk and they are 

 about three times longer than wide. These shields are hardly contiguous distally 

 and they afterwards separate divergently; it even happens sometimes, with the 

 largest specimens, that the shields remain distally separated by a narrow interval. 



The very minute plates of the margin of the disk extend uninterruptedly over 

 to the under face, where they remain small, very thick, and strongly imbricated ; 

 they are, even, sometimes more or less erect. The genital slits are fairly wide. 



The mouth shields are elongated, longer than wide. They are often lozenge- 

 shaped, with a truncated distal angle, and the widest part is more distant from the 

 proximal angle than from the distal side. It may also happen that the shields 

 offer a chief triangular part, almost as long as wide, and that the distal edge then 

 presents in its middle a more or less protruding rounded lobe. The adoral plates 

 are triangular, very thin inwardly, and hardly contiguous on the interradial median 

 line; they are very strongly widened outwardly with more or less concave sides. 

 The oral plates are small. The external oral papilla is conical, spiniform, with an 

 obtuse end which is obliquely erect; the internal papilla is thick, conical, and has 

 its end more or less truncated. A third intermediary papilla, which is thinner 

 than the preceding ones, conical and pointed, is seen on a slightly higher level. 



The upper brachial plates are large, much wider than long, with a rounded 

 proximal side, a wide and very convex distal side which is slightly protruding 

 in its middle; the lateral sides are narrow. The proximal and lateral edges often 

 are not very distinct from each other; the plate then takes an almost biconvex 

 shape with a rounded distal side showing in its middle a more protruding part. 



The first under brachial plate is small, trapezoidal, with a rounded and narrow 

 distal side, a widened proximal side, and divergent lateral sides. The succeeding 

 ones are pentagonal, rather small, with a very small proximal angle, slightly exca- 

 vated lateral sides and a straight or slightly excavated distal side. These plates are 

 a little wider than long; they are all contiguous. 



The lateral plates bear each six and even seven spines at the basis of the arms. 

 The first ventral spine is cylindrical, swollen at its basis, with a rounded end which 

 slightly exceeds the article. The length of the other spines rapidly decreases 

 down to the last dorsal. The second spine, at least as much developed as the first, 

 begins, at a small distance from the disk, to show at its end a bent and hyaline hook 

 which becomes very strong and joins the spine by a rather well-marked but broadly 

 rounded angle. The other spines are cylindrical with rounded ends, except the 

 last dorsal one, which is rather strongly flattened. The very peculiar character of 

 the second ventral spine was not pointed out by Ljungman in his first description, 

 but in the table of Amphiuridro, which he published in 1871, he says, "proxima ad 

 infimam geniculata . ' ' 



The tentacular scales, mounting to two, are small, subequal, and lying at a 

 right angle to each other. 



