BRITISH FOSSILS. 103 



not very different in size and nearly square, while in fig. 7 the 

 proportions are longer. All have the great curved spines placed 

 about the middle of the joint. 



In the perfect palpus (Plate XIII. fig. 9) the proportions of the 

 joints are as follows. The basal one is smaller than the second, 

 about two-thirds its length, and of a roughly triangular or trape- 

 zoidal shape, the base smallest. The second is longest half as long 

 again as its breadth ; the third and fourth much shorter, the 

 fifth only half as long as broad, and bearing one curved spine at its 

 outer angle, and the other (g) at its tip. The second, third, and 

 fourth joints are subcylindrical, convex on their outer margin, 

 and bear the curved spines about the middle of the joint. 



The terminal articulation (</), if it be a separate joint, consists 

 only of the curved process ; but it is probably only the opposite 

 spine of the fifth joint, seen obliquely, and in this view there would 

 be five joints only to the palpus, each joint bearing a pair of pro- 

 cesses, as is certainly the case in Plate XIII. fig. 11. 



The processes themselves are directed obliquely outwards and 

 forwards ; they are long, curved, sabre-shaped, and much com- 

 pressed, fully three times as long as the width of the joints, to 

 which they are attached by a swelled base. They are striated 

 longitudinally, the striae, eleven or twelve in number, sharply im- 

 pressed, not continuous except near the tip, but interrupted alter- 

 nately (Plate XIII. fig. 10) for wide spaces, so that the number of 

 striae appears little more than half what it really is. Nor are the 

 striae quite parallel to the sides, for they abut obliquely against the 

 concave side towards the tip of the process. Here and there some 

 striae are stronger than the rest. 



Near the base of the processes the striae are still more interrupted 

 and run into short impressed lines or puncta. 



Plate XIII. figs. 5, 6, 7, 11, and 18. These are from the UPPER 

 LUDLOW ROCK. Fig. 1 1 is a very perfect joint of the palpus, with 

 both spines attached ; and figs. 5 and 6 show the characteristic long 

 plicas ; fig. 7, part of a chela probably of this species. Fig. 6 at least 

 would answer best to one of the long joints of the antennae ; it is 

 but a cylindrical fragment of the proximal end, and has the 

 contraction which is visible in the corresponding joint of P. anglicus, 

 Plate IV. fig. 4 c. At this part the plicae are very numerous and 

 small; in the body of the joint they are large, prominent, and 

 elongate, and with the channel-like depression and its bounding 

 ridges, fig. 6a, magnified. They are somewhat unequal in size, and 

 set at more than their diameter apart from one another. 



