BRITISH FOSSILS. 



PLATE XII. FIGS. 7-16, 20, 21 ; AND PLATE XIV. 

 FIGS. 16-18. 



P. PEOBLEMATICUS. 



P. magnus, segmentis corporis ornatissimis, plicis minutis creberrimis 

 inter majores mixtis (segmento ultimo transverse, nee expanso, subtus 

 carina brevi mediana ?) : antennis dentibus longis, rectis, remotis. 



SYNONYM. P. problematicus, AGASS., in Sil. Syst. (1839), p. 606, pi. 4. 

 figs. 4, 5 (? Sphagodus pristodontus, AG., tooth only, ib. fig. 6). STRICKLAND 

 and SALTER, Quart. Journ. Geol. Soc., vol. viii. pi. 21. figs. 1, 2 ; Siluria, 

 2nd ed. pi. 19. figs. 4-6. 



As this is the principal, if not the only species in the true Upper 

 Ludlow Rock which has the usual semicircular ornamental plicae, it 

 is to this that the name problematicus should be given, and, fortu- 

 nately, on one of the minute original fragments figured in the 

 " Silurian System," the small intermediate plicae are to be seen 

 marking the species more definitely. 



The large chela, figured as above under this name, by the late 

 Mr. Strickland and myself, proves to be really an appendage of 

 this same species, at least it is always associated with it in the same 

 bed. Again, the antennary portions, fragments of body rings, bases 

 of the swimming feet, post-oral plate, &c., figured on Plate XII., 

 are all found in the Whitcliffe, Ludlow, or other localities of the 

 Upper Ludlow Rock, and clearly differ from the corresponding parts 

 in P. punctatus, the only other large species occurring with them, 

 as well as from those just described, which are characteristic of the 

 beds of passage above the top of the Ludlow series. P. problematicus 

 may now, therefore, be considered an established species, and the 

 cabinets of our Ludlow friends, Messrs. Cocking and Marston, have 

 furnished many of the materials. It occurs, too, in plenty, as Mr. 

 Lightbody's researches show, in the transition beds beneath the Old 

 Red Sandstone, Plate XIV. ; and Mr. J. Harley, to whom we are 



