BRITISH FOSSILS. 81 



' Antennas, Plate XII. figs. 1,2; Plate XIV. fig. 10. These re- 

 semble in general form those of P. anglicus, but have a more slender 

 shaft, tapering more quickly, and narrower and more conical teeth. 

 The teeth are intermediate in form between the species above men- 

 tioned and P. problematicus, the central one being long-lanceolate, 

 and the secondaries narrow, conical, and with coarse striae The 

 base of the fixed claw, Plate XIV. fig. 10, is furnished with a set of 

 stiff spines, as in P. problematicus, but the whole chela is propor- 

 tionably much shorter. 



Endognaths, Plate XIV. figs. 5, 6, 7. Of these there seem to be 

 two pairs, as in P. anglicus, and of very similar shape. The one 

 pair (fig. 5) resembles in all respects Plate VII. fig. 5, except that it 

 has the teeth more bent down. The joints of the palpus, like those 

 of P. gigas, have a squamose ridge along each side, and the ends of the 

 joints are bilobed. The second joint is three and a quarter times as 

 long as broad. This is nearly the proportion in P. anglicus, where 

 it is three times the breadth. 



The other pair of jaws (fig. 7) have their anterior margin more 

 curved, and the teeth set on a more convex edge than in P. anglicus. 

 The first tooth a is set more backward, thick, and curved at its base, 

 and all are more curved than in the Scotch species. 



The Post-oral Plate (Plate XII. fig. 3) may belong either to this 

 or to P. gigas. 



Base of Swimming Foot, Plate XIV. figs. 8, 9. These portions 

 are verv characteristic in all the species. In this the shape most 

 nearly resembles that of P. gigas, Plate IX. fig. 8, and the teeth are 

 short and blunt, as in that species, but the neck is shorter. From 

 P. anglicus, the shorter form, the short neck, blunt teeth, and con- 

 vex upper lobe (a) overhanging the teeth, distinguish it ; but the 

 sculpture raised into thick, prominent, boss-like plicse is almost 

 identical. The lower edge is tuberculate, and even spinous ; our 

 figure does not show this part. A little comparison of this specimen 

 with Plate VII. fig. 2, will show that both in the upper or front 

 edge (ft), and on the lower or hinder edge (6), the terminal lobe is 

 more prominent in P. ludensis. We do not know the other joints, 

 unless Plate XII. fig. 6, be the penultimate one. It has exactly 

 the form of that of P. gigas. 



Thoracic? Appendages! Plate XII. figs. 4, 5. The nature of these 

 is not understood, nor do these specimens show the characteristic 

 irregular base. But they differ specifically both from the similar 

 appendages in P. problematicus, Plate XII. fig. 16, and from the 

 more perfect one figured in Plate XIII. fig. 16, by their deep ter- 



[1.] F 



