DESCRIPTION OF THE SPECIES OF PTERYGOTUS 22 
Fig. 1 in Plate XIII. [Plate 24] occurs with the fragments 
of the species, and probably belongs to it, as its form is so elongated 
or compressed laterally (compared with those figured on Plate VII- 
[Plate 18], which belong to a broad-headed species). The length 
from the serrate edge a 4, to the end of the basal process £ is no 
greater than the breadth of the serrate margin ad. The general form 
is broad-falcate, the produced base / squareish, and the insertion of 
the palpus ¢ very near the serrate margin. This is beset with curved 
narrow teeth, six or seven of which are distinct in the upper half, 
and there are numerous smaller ones below. The teeth are articulated 
with the margin, not mere processes of it, as in the serrate base of the 
ectognath. 
Figs. 2, 3, 4, however, belong certainly! to P. acuminatus. Fig. 3 
shows the endognath a, seen only in part with a simple palpus 
attached cd, of which only two joints are preserved; the lowest ¢ 
broad and almost urceolate (not shortened, as in Plate VII. [Plate 
18] fig 9), and about as long as wide. The second @ is narrower ; 
minute plicae cover the base of both joints. Beneath this, and appar- 
ently attached to a distinct plate e, pressed closely upon a, and 
sculptured like it, is another and broader palp, of which only the 
basal joint is visible; and we must refer to a more perfect specimen 
(fig. 2, 2 a) for other details of this appendage. 
In fig. 2 the endognath a is seen to have a straight edge above 
with which the serrate margin forms an obtuse angle (about 120°). 
It is rather suddenly contracted where the teeth begin ; they are very 
oblique, narrow, conical, with a rounded base, and straighter than 
those of the separate specimen, fig. 1 (the latter is, however, as before 
said, probably the same species). 
The first two joints of the single palpus ¢ @ are quite distinct, 
and ¢ in fig. 2 a shows a toothed distal edge, such as is seen in the 
joints of fig. 4. The second palpus (probably attached to the crushed 
second maxillary piece) shows obscurely three or perhaps four broad 
joints at base fg, and then divides into a pair of jointed styles, 22% J, 
with tubercular or spinose joints. 
Fig. 4 explains this second appendage, it has a broken and 
obscure basal portion a (which may be part of the serrate basal 
joint?) followed by three broad joints 4 ¢ d, the second (4), being 
transverse, c and d are nearly square, thickened at their ends, which 
are ornamented by a crest of spiniferous tubercles. Similar tubercles 
1 As Prof. Huxley has described Plate XV. [Plate 26] fig. 1, in detail, I need only refer 
to it here (see p. 188.) It shows, I think, the single and branched palpi; but only one 
mandibular piece, with teeth, is visible on each side. 
