OPHIUEANS OF UNITED STATES NATIONAL MUSEUM. 27 



The diameter of the disk is 10 and 12.5 mm. respectively; the arms are 

 incomplete; in the larger specimen they are preserved to a length of 28 mm. 



The disk is somewhat thin and its outline is pentagonal. The dorsal face is 

 slightly convex, the ventral face is plane, and the edges are rounded. 



The plates of the upper face of the disk are large, few in number, very regularly 

 arranged. There is to be seen one centro-dorsal plate, fairly large, pentagonal, out 

 of which come a first circle of small interradial plates and a second circle of larger 

 radial plates. After the latter come two other radial plates which separate the 

 two radial shields of each pair, one of which is elongated, narrow, triangular, with 

 a truncated distal apex; the other, shorter, is also triangular, but wider than long, 

 with the proximal apex truncated. In the interradial spaces also, two plates 

 successively appear: One, pentagonal and wider; the other, quadrangular, nar- 

 rower, and more elongated. Beside these, two much smaller plates are observed 

 at the margin of the disk, which are visible also from the ventral face. The radial 

 shields are large, triangular, and separated on their whole length. All the plates 

 of the upper face of the disk are uniformly covered with rounded granules of a fairly 

 large size, but flattened, put close together but not in contact. 



The under face of the disk shows in the interradial space and out of the large 

 mouth shield a single plate, which is large, pentagonal, as wide as long, with 

 straight sides, and the obtuse distal angle of which reaches the outer margin of the 

 disk, where the two above-mentioned little plates are also to be seen. The genital 

 plates are fairly large and narrow, four times longer than wide. All these plates 

 are covered with granules identical with those of the upper face; these granules, 

 however, disappear in the proximal region of the genital plates and of the median 

 interradial plate; and they are lacking on the mouth plates. The genital slits, 

 which are found between the adoral plates and the mouth shield, are extremely 

 narrow, short, and scarcely visible. 



The mouth shields are fairly large, pentagonal, with an acute proximal angle 

 and straight sides; they are longer than wide. The adoral plates are fairly large 

 and two and a half times longer than wide, with parallel margins. The oral plates 

 are triangular, fairly high. The oral papillae, the outlines of which are very distinct, 

 amount to five or six on each side. The external papilla, located without the oral 

 plate, is large, wide, quadrangular, and longer than wide; the other papilla? are very 

 much lower: the second and third are rectangular, longer than wide, while the 

 other two or three are smaller. The odd terminal papilla is also very small. 



The upper brachial plates are visible only on the smaller specimen, and even 

 there they are altogether rudimental and scarcely distinct; they extend, however, to 

 almost the whole length of the arms. On the larger specimen, the first upper plate 

 alone is preserved, although it remains rudimental, and the following ones have 

 completely disappeared. 



The first brachial under plate is rather small, pentagonal, with an obtuse 

 proximal angle, and its distal border is slightly convex ; this plate is slightly wider 

 than long. The second plate is large, triangular, with an acute proximal angle 

 and a straight distal side; the lateral borders are sometimes bent into two small 

 sides, united by a very obtuse angle, which gives to the plate a pentagonal shape. 



