246 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
broad. Fig. 5 shows the closely squamate lateral edges of the 
segment, which are convex and rounded in the forward portion and 
sharply keeled behind. The front margin in both of these segments 
is contracted, for articulation with the previous joint, and has a broad 
groove running along its whole length. The hinder angles are a little 
produced. 
Penultimate segment, figs. 6, 7, 8, 9, and Plate IX. [Plate 20] 
fig. 15 —This joint is much wider than long, in the proportion of four 
inches and a half to two inches and a half; some specimens must 
have been fully five inches long, and therefore nine or ten broad. 
The segment is widest and flattest at the hinder end, the margins are 
compressed and keeled, except at the thickened and contracted base, 
and the angles (fig. 9) pointed and produced. The upper surface 
(fig. 7) is gently convex, but without any ridge, while the lower (?) 
fig. 6 has a short thick keel extending half way up. It terminates on 
the hinder margin of the segment, which is rather deeply notched at 
this point. The surface is thickly covered with plice, both above 
and below, but they are much more prominent on the lower (keeled): 
surface than on the other, where they are mere surface markings and 
often obliterated. They cover the whole of the segment, but are less: 
thickly placed towards the hinder margin, at least on the under side 
(fig. 6). The margin itself is tubercular. 
The squamate keeled lateral borders are ornamented with several 
(about four or five) rows of oblique thick plicae, more prominent and 
larger on the lower side ; these are continued from about the anterior 
fourth of the segment, where the keel commences, to the pointed 
hinder angle. Similar, but still larger, plice cover the central keel, 
Plate IX. [Plate 20] fig. 15a, and numerous shallow folds run 
obliquely backwards from the sides to the keel. 
Telson or Tatl-Jotunt, Plate IX. [Plate 20] figs. 16, 17. — The 
dimensions of this joint give the best indication of the size to which 
the species grew ; its length was full five inches and the width four 
and a half. The largest specimens of this part in P. anglicus, 
Plate V. [Plate 16] fig. 5, are rather longer but narrower. The 
general shape was that of a broad and pretty regular oval, but 
truncated at the base, and emarginate at the apex.! The under side, 
fig. 15 4, is flat, except at the origin of the joint, while it is somewhat 
convex ; the median line is even concave. Oblique folds or lines, 
like those on the penultimate segment, occur on the forward half. 
The upper side is also flattened, but furnished along its whole length 
1 Plate IX. [Plate 20] fig. 15, is the only specimen which shows the apex. Perhaps. 
there say have been a short central apiculus, as in P. azglecus. 
