238 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
fig. 2, deeply emarginate to receive a process from the fifth joint ¢ a. 
The inner side of this joint (serognathite), which is rather a difficult 
one to describe, is much narrowed, and terminates in an acute angle 
opposed to the wide basis of the outer margin. 
ca. Of the next joint (carpognathite) it is equally difficult to give 
a clear idea; its shape is irregular. It is somewhat crescentic on the 
upper surface, its outer side much the longer, and its distal margin 
oblique, nearly straight for the greater part of its length, but the 
outer angle truncated, and the inner notched. On the under side 
it follows the shape of the preceding joint, and has a prominent 
median process above to fit into the notch of it. Its distal margin, 
too, on this surface is sinuous, and less oblique than on the upper 
side. 
p. (and fig. 3). The penultimate joint (prognathite) is flattened (to 
form with the last, @,a swimming palette). Our largest specimen 
measures two and a half inches in length, by one and a half at its 
broadest part. It is somewhat quadrangular, but one-third broader 
below than above. Its outer edge is perfectly straight, longer than 
the inner, and terminating above as a narrow rounded lobe, behind 
which is a deep emargination, continuous with the curved outline of 
the inner margin. The latter is produced inferiorly into a subtri- 
angular lobe (3 c), broader than the superior process of the outer 
margin above described. The rest of the inferior border (@) is nearly 
straight, and forms almost a right angle with the straight outer 
margin. 
d. The terminal palette (dactylognathite) is broadly ovate, twice as 
long as broad, its apex rounded, its outer margin quite regular; the 
inner a little flattened above, leaving room for the play of the palette 
against the penultimate joint, as in the swimming crabs. 
The surface of the great basal joint is nearly covered with large 
plicee or squame, the convexity of which is outwards over the lower 
and hinder half, and inwards along the front margin. The other 
joints are more strongly ornamented, the plice coarsest on the 
exterior margin: on the three or four terminal joints they are only 
obscurely visible except on the margin. 
The margins of at least the two last segments are beautifully 
crenulated all round, with appressed serratures; these are largest 
at the apex and inner edge of the terminal swimming palette. 
Afetastoma, Plate VI. [Plate 17] fig. 7—The only piece which 
remains to be described is this large oval plate, deeply notched at 
the broader anterior extremity, regularly rounded on the sides, and 
