206 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
distinguish the present species from the following. The different 
portions may now be more minutely noticed. 
The carapace, one inch and a quarter in length, is half-oval, only 
one-fifth wider than long. The position of the long eyes. is very 
forward on the sides, and they somewhat interrupt the general oval 
contour. They are broadly crescentic and convex, placed half 
below (fig. 4.¢) and half above the margin of the head, and their 
extreme length is rather more than half that of the head. No lenses 
can be seen with the naked eye, but when magnified the appearance 
is that given in fig. 4d. 
Body Segments.—TVhe body in well-preserved individuals is barrel- 
shaped in front, the anterior or thoracic segments, taken together, 
measuring about one inch and three-quarters in length by one inch 
and a quarter broad. They are widely transverse, the anterior one 
being fully four times as broad as long, or even more. 
The second ring, as seen in a specimen not here figured, is five 
times as wide as it is long, the central part gently arched forwards 
in the middle, and at the sides the upper angles are produced forward 
into blunt lobes,! the outer margins being oblique, and their posterior 
angles are a little produced backward, particularly in the sixth or 
hindermost thoracic ring. 
The remainder, which are here reckoned as abdominal, are gradu- 
ally narrower, the seventh being only three times as wide as long, 
the tenth only once and a half, and somewhat narrower at the origin 
than the posterior edge ; the penultimate (eleventh) is squareish, only 
a little wider than long, also contracted at the origin and with the 
‘outer angles produced to lap over the rounded anterior edges of the 
caudal joint. A strong carina runs down this segment upon the 
upper side, but for the lower half only. 
The caudal joint (telson) is only two-thirds as wide as long, and 
nearly double the length of the penultimate one. It is rather wider 
behind, and strongly emarginate ; a deep furrow takes its origin from 
the notch, and continues more than half-way up. There is a low keel 
at the upper end joining that of the preceding segment, but only for 
a very short distance. 
The outer margins of the body and tail segments appear to be 
quite smooth, not serrate or crenate as in several other species. 
The thickness or rotundity of the joints we have no means of 
ascertaining. 
The sculpture is minute and characteristic, but is only visible at 
1 This form of the second segment is common to all the species, see fig. 13 of this Plate, 
and Plates IV., X., XIIL. [Plates 15, 21, 24], &c. 
