1857.1 HUXLEY PYGOCEPHALUS COOPERI. 365 



tinuous with the under edge of this joint, is a flat, broad plate (2"), 

 with an oval, distal contour, and presenting what appear to be 

 traces of a fringe of setae on one side. Regarding the quadrate 

 joint and this plate as one part, they form a scoop-like scale, ^ inch 

 long by ^ inch wide. Lying in the hollow of the scoop, and articu- 

 lated either with its base or with the basal joint itself, is a fusiform 

 mass (2') divided by two constrictions into three joints, the middle one 

 being shortest and subquadrate, while the inner and outer are conical. 

 The outermost passes into a cylindrical multiarticulate filament, whose 

 extremity is buried in the matrix. A longitudinal groove furrows 

 the outermost articulation and is continued on to the filament, giving 

 rise to an appearance of division — but I believe this to be acci- 

 dental. 



On the left side the appendage has a similar structure, but is less 

 perfectly preserved. 



The small appendages (1') of the quadrate disk lie between the 

 large ones. They consist of two proximal subcylindrical short joints, 

 which do not equal more than half the length of the scale of the 

 outer appendage ; beyond these, traces are visible of another joint, 

 and of a long, multiarticulate, terminal filament. 



On the one side of the specimen, the matrix comes close up to 

 the edge of the quadrate disk ; but on the other, an elongated, nar- 

 row plate («?), with a somewhat excavated anterior margin, joins it 

 at the base of the scale-like appendage. This plate is exposed for 

 about -rAynds of an inch in width and |^ths of an inch in length. Its 

 outer margin is straight, and slopes outwards so that proximally it is 

 ^ths of an inch distant from the axis of the specimen, while distally 

 (or at the base of the scale) it is only i inch distant from the same 

 imaginary line. A narrow triangular space, occupied by matrix, 

 is left by the divergence of the plate from the central part of the 

 body, and lodges three of its appendages on this side. 



The central part of the body (6) measures about half an inch in 

 length ; it is narrowest towards the quadrate disk, widest at the 

 opposite extremity, where it attains nearly ^^ths of an inch, and 

 is divided into seven segments of nearly equal length, but gradually 

 increasing breadth. Each segment appears to consist of a median 

 plate, separated by an oblique furrow from two lateral plates ; the 

 latter are quadrate, with their margins concave outwardly and to- 

 wards the quadrate disk ; convex and somewhat raised, towards the 

 semicircular disk. The median plate increases in width from the 

 segment nearest the quadrate disk, which we may call the first, to 

 the last. The lateral plates are nearly of the same size throughout, 

 except the first pair, which appear to be larger than the others. 



Attached to the outer boundaries of the lateral plates, seven ap- 

 pendages are observable on the left side, but only six on the right. 

 In the more perfectly preserved appendages (fig. 1 c) there may be 

 distinguished a short, proximal, convex, subcylindrical joint, followed 

 by at least three other slender and delicate articulations ; of these 

 the proximal one is the longest, the terminal next in length, and the 

 middle one shortest. 



