84 



BRITISH FOSSIL CRUSTACEA. 



(fig. 10), which is in close juxtaposition, and has a fragment of the fifth joint attached 

 to it. 



The fourth and fifth joints closely resemble those in P. anglicus (see pi. vi, op. 

 cit), 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. (now Eurypterus) punctatus, the lobes being apparently equally prominent, and the 

 distal or outer end is trilobed ; this is partly seen in fig. 1 0, but much better in fig. 1 1 , 

 where the outer lobe is pointed and prominent, the middle one rounded and shallow, 

 and the inner 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 squamae, and the surface of the preceding joints (the fourth especially) has close 

 and rather elongate plicae. 



Of the terminal palette there is no trace ; its probable shape is given in the dotted 

 outline (by Mr. Salter, in pi. ix, fig. 10, op. cit.). 



Only the metastoma (pi. ix, fig. 13, Mem. Geol. Surv., Mon. I) remains to be described. 

 It is greatly like that of P. anglicus (pi. vi, op. cit.), and chiefly differs in the more con- 

 tracted base and large open plicae of the surface. The notch is somewhat deeper. It 

 may have been smooth over the hinder portion (as in pi. xii, fig. 3, op. cit.), which is 

 the same or a closely allied species, and may be noticed here, though possibly it belongs to 

 P. ludensis, above described. (See Woodcut below, Fig. 18.) 



^,— — 



Fig. 18. — Metastoma, or post-oral plate, belonging either 

 io Pt. ludensis, or to Pt. yigas, from the " Passage- 

 beds" at Ludlow. 



* A part of the sculpture magnified. 



Fig. 19. — Imperfectly preserved Metastoma referred to 

 Pt. problematicus, Upper Ludlow Rock, Ludlow. 



