128 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



triangular, with a rounded proximal angle; they are twice and a half longer than 

 wide and their length is about equal to half the radius of the disk. These shields 

 are absolutely bare and their surface is deprived of stumps, except near the external 

 edge, which may show two or three. The two shields of each pair are parallel 

 to one another, and they are widely separated by two or three rows of plates. The 

 under face of the disk is covered with small, imbricated, equal plates, the outlines 

 of which are fairly distinct, and which may each carry a little elongated and conical 

 granule. These granules appear chiefly near the outline of the disk, but they do not 

 occur, however, until near the radial shields, chiefly on the larger samples. The 

 genital slits are wide and very conspicuous and extend from the margin of the disk 

 to the mouth shields. 



These shields are much wider than long, with a very obtuse and rounded 

 proximal angle, which is limited by two slightly incurved sides; the lateral angles 

 are more or less thin and sharp; the distal side is convex and forms a lobe more or 

 less protruding into the interradial space. According to the respective forms of 

 this distal lobe and of the proximal angle, the shields are either triangular, which is 

 the most frequent case, or lozenge-shaped. The rather large adoral plates are thick, 

 two and a half times longer than wide, and bent in the shape of a crescent; they 

 are narrower toward their distal end. The oral plates are triangular and rather 

 small. The oral papillae generally amount to four and are arranged in a regular 

 row; they are rather thick and covered with sharp denticulations, which are very 

 small and dense; the two internal papillae are narrow and the two external ones 

 are more widened. To these papillae are sometimes added two smaller ones which 

 are intercalated between the former. The odd terminal papilla is larger than the 

 others, wide, rounded, and rough. 



The upper brachial plates are fairly large, triangular, with a rounded proximal 

 angle and a convex distal side; they are a little wider than long and they sometimes 

 become a little campanuliform; from the second one upward, they are separated 

 by a very wide interval. One meets sometimes on the first three or four articles 

 a little rounded supernumerary plate at the base of the chief dorsal plate, but I do 

 not observe this character except on the largest specimen, and I think it is due to 

 age; it is important to note that neither the young nor the middle-aged ones show 

 any indication of it. 



The first under brachial plate, which is rather large, is a little longer than wide, 

 its proximal side being larger than its distal side. The four or five succeeding 

 plates are large, very much widened, wider than long, triangular, with a very 

 obtuse proximal angle and a strongly convex distal side. The width of the under 

 plates then decreases progressively and they very soon become as long as wide; at 

 the same time, they assume a pentagonal shape with two distinct lateral sides and 

 a rounded distal side; they are broadly separated from each other from the second 

 one upward. 



The protruding lateral plates carry five spines each. The first two ventral 

 spines are shorter than the article; the third one is almost as long as the article, 

 the fourth is larger, and the fifth reaches about one and a half articles. These 

 spines are strong and thick, cylindrical, with an obtuse and rounded end, except 



