86 BRITISH FOSSILS. 



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 pen- 

 ultimate segment, occur on the forward half. The upper side is also 

 flattened, but furnished along its whole length 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 de- 

 creasing 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 plicae, except near the base, where they are numerous 

 and prominent both on the upper and under sides. 



Appendages. 



Ghelate Antennae, Plate IX. 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 (6) 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 striae 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 striae parallel. 

 These striae 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 6, and one a great 

 striate tooth c* apparently the median one (see Plate VI. 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. ; and the second maxillary piece is more curved 

 anteriorly. Mr. Banks' cabinet contains both. 



Of the palpi (Plate IX. fig. 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 



* A similar tooth (?) has heen figured in P. problematic. See Quart. Geol. Journal, 

 vol viii. pi. 21. fig. 26. 



