DESCRIPTION OF THE SPECIES OF PTERYGOTUS 209 
m, (Werognathite) rudely trigonal, its hinder base meeting the 
produced articular lobe of the large penultimate joint /. 
[Either this or the next joint ca bears the long three-jointed 
filament 4 The forward salient angle of the limb is 
formed between this and the succeeding joint] 
ca. (Carpognathite) triangular ; its convex base outwards, its apex 
inwards against the process of /. 
p. (Prognathite.) All the preceding joints, except the great basal 
one, do not quite equal the length of the penultimate joint £. 
It is oblong, but narrower at the base, which is oblique, with 
the hinder edge produced into a process (s), which reaches 
the fourth joint (#2). The outer margin is rather convex, the 
inner a little concave, and the apex deeply and pretty equally 
bilobed, to receive the terminal joint. 
ad. (Dactylognathite.) A regularly ovate palette, as long, measured 
along the middle line, as the penultimate joint, and nearly as 
broad ; it is attached to it by a prominent tubercle. 
No sculpture has been observed on the limbs. 
Metastoma or Post-oral plate, figs. 1, 10—These cordate plates 
(referred to the posterior margin of the mouth, p. 182) occur with all 
the species. The piece is nearly of the same narrow ovate shape in 
this as in P. perornatus, fig. 15, but only one-third the size, deeply 
cordate, with a sharp notch and rounded lobes in front, and with 
the base also rounded ; the width is about half the length, the lobes 
are covered thickly with rather large semicircular plice, which are 
absent from the other parts of the plate. 
Fig. 1 shows this plate in its natural position, and fig. Io a 
detached plate as commonly found. The latter occurs in a group 
with a pair of antenne, of which fig. 6 is one, and with the swimming 
foot, fig. 8; all probably therefore belong to the same individual. 
Our specimens are so much altered in shape by pressure, that it 
is difficult to point out any real variations in form. Fig. 2 appears 
to have the true general shape. Fig. 1 is evidently compressed 
laterally, as is the caudal joint, fig. 11 ; while fig. 12 shows that joint 
shortened by pressure from behind forwards. Fig. 4 is reduced in 
length by the same cause, and appears too broad in proportion for 
the length. 
VOL. II. a 
