DESCRIPTION OF THE SPECIES OF PTERYGOTUS 247 
with a great central keel, rather thick at its origin, but becoming 
narrower and more elevated (six-tenths of an inch high in the centre), 
and then decreasing towards the tip. 
Sculpture as in the preceding segment. The blunt ridge of the 
central keel is covered with small squamate plates, and the margins 
have four or five rows of oblique elongate ones. The general surface 
is bare of plice, except near the base, where they are numerous and 
prominent both on the upper and under sides. 
Appendages. 
Chelate Antenne, Plate IX. [Plate 20] figs. 1, 3. — Fragments 
only are yet found; the large base of the fixed claw, fig. 1, is about 
five inches long to the first tooth (in the largest P. anglicus it is not 
more than three inches and a quarter), and one inch ten lines broad 
(nearly of equal breadth throughout). The articulating edge (a) is 
long and oblique, the joint narrowing considerably into the serrate 
claw. Of this portion (4) there is but little preserved, but it shows 
the chela to have had broad (probably subovate) cutting teeth, as 
well as numerous close set smaller ones. These last are short-conical 
near the base of the fixed claw, and coarsely striated parallel to their 
sides, the stria branching from above downwards. Further out (as 
shown in the separate specimen, fig. 2, which may be the free claw) 
the smaller teeth are lanceolate and narrow, and the striz parallel. 
These striz are very closely set, much more so than in any other 
species. These teeth appear to have been irregular in size, and much 
crowded; a third specimen (fig. 3) shows three kinds,—the small 
lanceolate one a, larger subovate secondary ones J, and one a great 
striate tooth c,! apparently the median one (see Plate VI. [Plate 17] 
fig. 5), which is coarsely ribbed, and is besides serrate on the inner 
edge. 
The endognath has somewhat broader and shorter teeth than that 
figured in Plate VII. [Plate 18]; and the second maxillary piece is 
more curved anteriorly. Mr. Banks’ cabinet contains both. 
Of the palpi (Plate IX. [Plate 20] figs. 5-7) only fragments are 
left. Fig. 5 shows four joints connected, but all compressed in a 
direction perpendicular to their length. Their diameter is half an 
inch, and their proportions may be compared with those shown in 
Plate VII. [Plate 18] fig. 4. The second joint d is rather longer, 
and the third ¢ not quite so long as in P. anglicus. The other figured 
1 A similar tooth (?) has been figured in P. problematicus. See Quart. Geol. Journal, 
vol. viii. pl. 21, fig. 2d. 
