208 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
given as a woodcut. It is contracted in width as compared with 
the shape in some other species. The anterior serrate lobe @ is. 
narrow, and with sharp curved articulated teeth. The lamina 7 is. 
oblique and sub-triangular ; and the palpus, set on rather far back 
from the serrate border, has a small quadrate basal lobe ¢ followed 
by a longer one @; the third and fourth (e/) are linear, and several 
times as long as broad. The terminal joints are still longer, as seen 
in Plate I. [Plate 12] fig. 1 ¢ (compare this with Plate VII. [Plate 18] 
figs. 4, 5). 
Epistoma and Labrum.—oOf the large semicircular piece which 
lies in front of fig. 1, and which has evidently been shifted from the 
under side of the head, we can only judge the true position by com- 
paring it with other species (A. perornatus, for instance, fig. 16, in 
which the mid-lobe a of the organ is seen to be of an ovate shape) ; 
also in Plate XV. [Plate 26] fig. 2 4 where a similar piece lies in 
front of the head. 
In fig. 1 the semicircular outline probably corresponds to the 
hinder free margin (of much more angular shape) in the epistoma of 
P anglicus, Plate II. [Plate 14]. The mid lobe @ is obscurely 
marked out, but is of an ovate shape ; its insertion not very clearly 
seen. 
Ectognaths.—Fig. 3 shows these organs in their place at the 
lower angle of the carapace, drawn forward as for a stroke; the 
forward bend of the limb at the fifth joint ca, and the great serrate 
bases 0 indistinctly visible through the crust. Fig. 9, with part of 
the carapace broken away, has both limbs in place, and figs. 1 and 2 
show these natatorial feet laid backward close along the body. Fig. 8, 
magnified at 8a, is an entire separate ectognath. The several joints 
of this appendage are :— 
Basal Joint (coxognathite), figs. 4 ¢, 8 co—The great lower lobe is 
wide, and of a spherico-triangular shape, the inner margins as well as 
the outer and base being all convex. The neck is suddenly con- 
tracted and short, and the serrate terminal lobe transverse or oblong, 
greatly oblique and overlapping the opposite edge (not vertical as in 
P acuminatus, Plate II. [Plate 13]). Its toothed margin is curved 
and set with thirteen small teeth. 
The other joints are attached low down, ze, below the outer 
margin of the basal joint, and consist of— 
b, (Basignathite) short and broad-linear. 
2. (lschygnathite) narrow triangular, produced a little at the 
hinder angle (but not forming a lobe as in Plate VI. [Plate 17] 
fig. 1). 
