the following, the palette. It is subrectangular in general outline, its length is one fifth longer than the width, the proximal and distal sides both deeply notched for articulation. The upper angle of the proximal side is evenly rounded, the lower much produced to meet a corresponding notch in the preceding segment. The lower part of the distal side is produced into a triangular plate about one third as long as the segment and separated from it by a transverse suture. The other upper part of the distal margin is nearly straight. The eighth segment is a very long oval, twice as long as wide, the distal end being the more slender. The terminal segment is subcircular in outline and relatively large.
Figure 58 Diagram of dorsal view of left swimming leg
The metastoma is heart-shaped in outline and relatively short. The frontal margin is the longest; it seems to be slightly emarginate, but the preservation is not clear enough to determine this point. Length and width of plate nearly equal. The antelateral angles are well rounded and the sides contract in a gentle curve to the blunt posterior extremity.
Genital appendages. Of these only the female have been seen in two examples. In the older of the two the appendage begins with two triangular (or subpentagonal) basal members, not seen in the younger individual, as the sutures which separate them from the opercular plates are not developed. These plates inclose an elongate sagittate base similar in shape to that of Pterygotus buffaloensis. At the posterior angles of the latter two semicircular lobes are observable which probably covered the genital openings. From it proceeds the slender middle portion which is convex along the median line and flat along the borders. The distal extremity is seen in the younger specimen. Here it consists of two converging obtuse pieces with parallel inner and converging outer sides. The basal portion which is sagittate in the older individual is rounded or in-
