DESCRIPTION OF THE SPECIES OF PTERYGOTUS 229 
entire length could not have been less than six, and from the size of 
the epistoma and some other parts probably reached eight feet in 
length! There are no living Crustacea which can match this in 
bulk. 
And it was apparently of considerable thickness, almost cylin- 
drical; the crust, however, appears to be very thin and paper like, 
and only thickened where requisite for the attachment of strong 
muscles, as in the swimming feet ; or along the ridges and margins,— 
the serrated parts of the mouth, &c. 
The carapace, now first described from a young specimen, 
measures six inches and a half long and fully nine inches wide at 
the broad base, but narrows considerably towards the front, where it 
is less than five inches and a half broad. 
Our figure shows it compressed a little obliquely, but, allowing 
for this, it is not far from the true shape, and it is probable that 
not much of the margin is lost on the right-hand side, while enough 
remains of the other to indicate that the outline was somewhat 
curved. Two other specimens in Lord Kinnaird’s cabinet show the 
curved outline. The eyes are distinctly visible on each side, and are 
as large as crown pieces. 
The head must have been considerably more convex than at 
present, since in our flattened specimen it is corrugated all over; it 
is sub-pyramidal in shape, truncate or but slightly arched in front 
between the eyes, and concave posteriorly. The side margins (so far 
as visible) and the front are strongly crenate, but not tubercular ; 
the general surface appears smooth or minutely punctate, but not 
anywhere marked by plice. The eyes occupy the outer angles of 
the head ; they are oval, an inch and a half in the largest diameter, 
and about an inch broad. The lenses are rather large, about eight 
rows in one-tenth of an inch, and in this pressed specimen are 
rhomboidal rather than hexagonal, at least in arrangement ; this may 
be due to pressure only. 
The entire head, compared with that of P. acuminatus, is broad 
and short, and much narrowed in front, so as to be intermediate in 
shape between that square-headed species and the forms with semi- 
oval carapaces. The eye is much larger in proportion. 
Epistoma and Labrum, Plate III. [Plate 14] figs. 2-5 (6?).— 
This piece, which is the epistoma or under side of the front of the 
head, occurs in tolerable plenty, and is the portion formerly. supposed 
to be the carapace itself (see p. 171). From a very perfect and large 
specimen in the British Museum, a reduced figure (fig. 6) is added, 
which justifies the inference above drawn as to the great size of 
