DESCRIPTION OF THE SPECIES OF PTERYGOTUS 245 
As the fragments indicate a species of the largest size, the above 
specific name will not be inappropriate. The size of the chelate 
antenne exceeds that of any known species. 
There are two species in the Kington beds, P gigas and P. prob- 
lematicus, and it was of course possible that some of the parts 
assigned to the former might belong to the latter species. The 
subsequent discovery of nearly all the parts of P. problematicus shows 
that in this instance the fragments have been rightly collocated. 
Head or Carapace, Plate VIII. [Plate 19] fig. 1.—Nearly semi- 
oval, convex, the width three inches and three quarters at the broad 
base, probably greater than the length. The specimen being im- 
perfect behind, the true length is not known, but the portion preserved 
is three inches and a quarter long. The eyes are very large, three 
quarters of an inch long, oval and prominent beyond the margin. 
They are placed very near the anterior end, and the space between 
them on the margin is about an inch and three quarters, while 
between the convex inner edges of the eyes it is about an inch and 
a half. The anterior border is arched and very slightly angular in 
front, with a crenulate edge. The sides are convex (their margin not 
visible). 
In the centre of the carapace, and forming an equilateral triangle 
with the eyes, is an elongate tubercle. The general surface appears 
somewhat rugose. 
Epistoma, fig. 2—The proportions of this plate and its sculpture 
are very like those of P. anglicus ; and the specimen figured indicates 
this part to be quite as large as that in Plate III. [Plate 14] fig. 7. 
The plice on the upper or front portion (a) are crowded, and but 
slightly curved ; those further back are semicircular or even semioval, 
while those near the apex of the side lobes are narrower and pointed 
as in the cognate species. Similar but smaller plica occur down 
the centre lobe, which does not appear to have prominent elongate 
scales, nor is it convex as it is in P. anglicus. Its base c is broad and 
spear-shaped. 
Body Rings.—The anterior body rings, fig. 3, bear the squame 
only on their front half, and these are less curved and less crowded 
than in the corresponding segments of P. anglicus. The edge of the 
plice is thickened. Figs. 4 and 5 must represent large segments 
from a portion of the body further back than fig. 3, for the squame 
cover the whole lower surface of the segment (fig. 5), and the greater 
part of the upper side (fig. 4). They are greatly more convex than 
in the Scotch species, the posterior ones especially being parabolic 
or even pointed in form, frequently three-tenths of an inch long and 
