BRITISH FOSSILS. 87 



their proportions may be compared with those shown in Plate VII. 

 fig. 4 The second joint d is rather longer, and the third e not 

 quite so long as in P. anglicus. The other figured fragments are 

 less distorted ; fig. 6 shows the fourth joint fully one inch and a 

 half long, with the tip expanded and bilobed. In fig. 7, one of the 

 lobes bears a fringe of spines. All the joints show elongate squamse 

 on their outer side. 



Svjimming Foot, Plate IX. fig. 4-9. The great basal joint, 

 fig. 8, with its serrated tip, closely resembles in form and sculpture 

 that figured in Plate VII., the chief difference being the greater 

 width of the foliaceous base, and the more backward position of the 

 notch at the point of attachment for the succeeding joints. The 

 serrate terminal lobe, figs. 4 and 9, has broad stout teeth, as usual, 

 thirteen in number, slightly curved, the uppermost broader and 

 shorter than the rest, the lowest b a rounded lobe as broad as the 

 two preceding teeth taken together. The teeth are shorter than in 

 P. anglicus, especially the upper ones, so that the outline of the 

 serrate edge is more curved. The perfect specimen is only three inches 

 and a half long by two and three-quarters broad, but fragments 

 indicate a size equal to the largest specimens of the Scotch 

 species. 



Of the other joints of the swimming foot only two or three 

 specimens (fig. 10-12) have occurred. Fig. 30 shows the upper 

 surface of the right-hand swimming foot, with two complete joints : 

 the fourth (m) and fifth (GO), with a portion of the great penulti- 

 mate joint p*. The latter joint is better shown in another frag- 

 ment, fig. 10, which is in close juxtaposition, and has a fragment 

 of the fifth joint ca attached to it. 



The fourth and fifth joints closely resemble those of P. anglicus 

 (see Plate VI.), but the form of the penultimate or propodite is as 

 usual characteristic. It is oblong, two inches and a half in length by 

 one and a half broad, and is but little broader at one end than the 

 other. The upper or proximal end is deeply bilobed, as in P. punc- 

 tatus, the lobes being apparently equally prominent, and the distal 

 or outer end is trilobed ; this is partly seen in fig. 10, but much 

 better in fig. 1 1, where the outer lobe a is pointed and prominent, 

 the middle one rounded and shallow, and the inner c truncate : 

 the last forms nearly a straight line ending in a sharp angle against 

 the straight inner margin. 



Both outer and inner margins of the penultimate joint are serrate 

 with elongate appressed squamse, and the surface of the preceding 

 joints (the fourth especially) has close and rather elongate plicse. 



