262 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
The Suvmming Feet (Plate XI. [Plate 22] figs. 12-15) are very 
different in proportion to those of P. anglicus, the terminal joints 
occupying a considerably greater length, and being abruptly wider 
than the rest. Of the great basal joint (co in fig. 5) but little is pre- 
served, but a larger specimen, fig. 12, shows it to have been roughly 
squamose, especially along its basal edge, the narrow squamz project- 
ing as small spines, the rest of the surface is closely imbricated with 
smaller plice. Pl. XIII. [Plate 24] fig. 14, is very possibly the 
serrate inner lobe of this joint. The second joint @ is large in pro- 
portion to the rest, and widens from the base to its truncated apex. 
The third 7 is subtriangular, the blunt apex of the triangle being 
anterior, and the edge articulating with the next joint nearly straight 
or but slightly curved. The fourth joint, on the contrary, is an obtuse 
triangle, of which the broad base is forward and moderately arched, 
but not projecting as in P anglicus. It contracts rapidly behind, 
where it has a narrow deep notch to receive the articulating process 
of the next joint. This, ca, is the fifth, a remarkably short wide 
articulation, almost buried in the concave edge of the great penultimate 
joint, and curved to follow the convex border of the triangular fourth 
joint. It is marked by a strong transverse ridge. All these joints 
may be seen in figs. 5 and 13, but in a far less perfect state than 
in the fine specimen, fig. 13, presented by my young friend Mr. 
R. Lightbody, jun., of Ludlow. The penultimate joint f is very large, 
nearly three inches long, and about half as broad. It is oblong, with 
two rounded unequal lobes, and deeply notched at each end (the 
distal notch at the end being the deepest), so that the joint overlaps. 
the proximate joints at either end. The hinder margin of the joint 
is more convex at first, then somewhat excavated, while the anterior 
margin is straight, or nearly so: the hinder lobes at both ends are 
larger than the anterior ones, the proximal one, which overlaps the small 
fifth and fourth joints, being broader and rounder, and the distal one, 
which abuts against the terminal palette, being long and narrow. 
The terminal joint (@) is very long, nearly three inches by nine- 
tenths of an inch wide, elongato-lanceolate, but rounded at the tip, its 
anterior margin a little convex, and plain-edged half way down, the 
posterior slightly concave and rather strongly serrate,—the serra are 
shallower on the anterior margin, and deepest round the tip. 
Locality —Church Hill, Leintwardine, in LOWER LUDLOW ROcKk ; 
Whitcliffe, Ludlow, UPPER LUDLOW Rock ; Kendal, Westmoreland ;. 
fragments in UPPER LUDLOW ROCK. 
J. W.S. 
January 22, 1859. 
