OPHIUKANS OF UNITED STATES NATIONAL MUSEUM. 35 



obtuse proximal angle, its lateral borders are parallel and its distal side is straight; 

 the second plate, which is located near the margin, is smaller, transversely widened, 

 and wider than long. The radial shields are large, longer than wide, polygonal and 

 sometimes distally rounded; proximally they touch the corresponding primary radial 

 plate and they are in contact with one another on two-thirds of their length; distally 

 they are separated by a little triangular plate. All these plates are slightly convex, 

 but they do not offer the slightest trace of tuberosity or swelling, such as is observed 

 in 0. pulchettum; their surfaces are covered only with fine granulations, which are 

 smaller on the plates of the primary rosette and become a little more conspicuous 

 on the plates of the disk margin, where they are, however, less marked than on 

 the arms. 



The under face of the disk is very much reduced in the intcrradial spaces, owing 

 to the considerable widening of the first two brachial articles; this reduction is, 

 however, less marked than in 0. pulchellum. The middle of each of these spaces is 

 occupied by a large elongated plate succeeding the mouth shield and contiguous to 

 it along its proximal border; this plate, which is narrow in its proximal part, grows 

 wider and wider, so that its distal border, strongly convex, is two or two and a half 

 times wider than the proximal side; the lateral borders are divergent and straight. 

 The distal side of this median plate extends slightly under the interradial plate 

 which occupies the margin of the disk on the upper side, and may be seen when 

 looking at the Ophiuran from the upper side. On each side of the median plate 

 there is a very large and elongated genital plate. The remnant of the under face is 

 occupied by a little triangular plate. The genital slits are small and very short, 

 not exceeding the base of the first lateral brachial plate, but they are, nevertheless, 

 easily recognized ; they are slightly fusiform. 



The mouth shields are distant from the mouth, owing to the width of the oral 

 and adoral plates, and their middles lie nearer the margin than the center of the 

 disk. They are rather small, pentagonal, about as long as wide, with a fairly 

 open proximal angle limited by two straight sides; the two succeeding sides are 

 about as long as the preceding ones; they join outwardly with a very short and 

 straight distal border. The adoral plates are fairly large, about twice and a half 

 longer than wide, with parallel sides. The oral plates also are well developed and 

 twice longer than wide. The oral papilla? are not distinct and they form a thin, 

 uninterrupted fringe along the oral plates. 



All the plates of the under face of the disk are covered with fine granulations, 

 which become a little stronger toward the margin and appear still more so on the 

 brachial plates. 



The arms are very broad at their bases, but they always remain quite distinct 

 from the disk; they are relatively short and their length is equal to the diameter 

 of the disk. I count no more than eight brachial articles when looking at the 

 Ophiuran from its upper face, and nine on the under side. The first upper brachial 

 plate is very much wider than long, its proximal side being concave, and its distal 

 side convex; it is in contact with the triangular plate which separates the distal 

 parts of the radial shields. The following plates, which very soon grow extremely 

 small, are triangular; with an obtuse proximal angle and a convex distal side; they 



