248 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
fragments are less distorted ; fig. 6 shows the fourth joint fully one 
inch and a half long, with the tip expanded and bilobed. In fig. 7, 
one of the lobes bears a fringe of spines. All the joints show elongate 
squamz on their outer side. 
Summing Foot, Plate IX. [Plate 20] figs. 4-9—The great 
basal joint, fig. 8, with its serrated tip, closely resembles in form and 
sculpture that figured in Plate VII. [Plate 18], the chief difference 
being the greater width of the foliaceous base, and the more backward 
position of the notch at the point of attachment for the succeeding 
joints. The serrate terminal lobe, figs. 4 and 9, has broad stout teeth, 
as usual, thirteen in number, slightly curved, the uppermost broader 
and shorter than the rest, the lowest 4 a rounded lobe as broad as the 
two preceding teeth taken together. The teeth are shorter than in 
P anglicus, especially the upper ones, so that the outline of the 
serrate edge is more curved. The perfect specimen is only three 
inches and a half long by two and three-quarters broad, but frag- 
ments indicate a size equal to the largest specimens of the Scotch 
species. 
Of the other joints of the swimming foot only two or three 
specimens (figs. 10-12) have occurred. Fig. 10 shows the upper 
surface of the right-hand swimming foot, with two complete joints ; 
the fourth (#7) and fifth (ca), with a portion of the great penultimate 
joint p*. The latter joint is better shown in another fragment, fig. 10, 
which is in close juxtaposition, and has a fragment of the fifth joint 
ca attached to it. 
The fourth and fifth joints closely resemble those of P. anglicus 
(see Plate VI. [Plate 17]), but the form of the penultimate or 
propodite is as usual characteristic. It is oblong, two inches and 
a half in length by one and a half broad, and is but little broader at 
one end than the other. The upper or proximal end is deeply 
bilobed, as in P. punctatus, the lobes being apparently equally pro- 
minent, and the distal or outer end is trilobed; this is partly seen in 
fig. 10, but much better in fig. 11, where the outer lobe @ is pointed 
and prominent, the middle one rounded and shallow, and the inner 
¢ truncate: the last forms nearly a straight line ending in a sharp 
angle against the straight inner margin. 
Both outer and inner margins of the penultimate joint are serrate 
with elongate appressed squame, and the surface of the preceding 
joints (the fourth especially) has close and rather elongate plice. 
Of the terminal palette we have no trace; its probable shape is 
given in the dotted outline. 
Only the mefastona, fig. 13, remains to be described. It is greatly 
