90 BRITISH FOSSILS. 



indebted for much valuable help, has been fortunate enough to 

 detect its fragments far up in the cornstones of the Old Red itself, 

 a higher limit than the genus had been known before to attain. 



[If the large fragments from the transition beds above quoted, 

 and figured on Plate XIV., be of the same species, as the sculpture 

 indicates, the body segments attained a very large size, nearly three 

 inches from back to front. As it is possible these may belong to a 

 different species, I will describe these portions first. 



Carapace (T), Plate XIV. fig. 16. A fragment, three inches by 

 two and a half, has the surface sculptured, unlike the body rings, 

 i.e., much more finely marked, and without the regular increase in 

 size and curve of the plicae backwards. The anterior ones are 

 nearly as much bent as the hinder ones though smaller all are but 

 slightly prominent, and are covered by numerous smaller plicse. 



Body Rings, Plate XIV. fig. 17. One of the broad abdominal 

 rings, two inches and three quarters from back to front : the articu- 

 lating front margin is rather deeply concave, and its edge is 

 obscurely striate longitudinally (like fig. 3). The plicse are very 

 numerous and close-set, not so large as in P. anglicus, or so straight 

 on the forward edge, where, however, they are very closely packed. 

 They are more open posteriorly, and cover more than half the seg- 

 ment, interspersed with very numerous minute semicircular plaits. 



Another piece (fig. 14) is here considered as belonging to this 

 species, but it only shows the interspersed plicae over part of the 

 surface : and it quite possibly belongs to P. ludensis, or even to a 

 new species. 



Penultimate Joint, Plate XIV. fig. '.18. Of this we have only 

 the lower surface ; and as the plicae are restricted to the upper 

 portions, and only a few small ones are interspersed, it is possibly 

 not P. problematicus, but of the same species as fig. 15, mentioned 

 above. The width is greater than that of the same joint in P. an- 

 glicus or P. ludensis, being three inches and a half, while the 

 length is only two and a quarter, (or as fourteen to nine,) which is 

 about the proportion in P. gigas. The joint is not expanded 

 posteriorly as in that species, and the plicse are semicircular, not 

 pointed, on the lower side.] 



In the true Ludlow rock but few body joints have been met 

 with, the two best are figured from Mr. J. Harley's collection, viz., 

 Plate XII. fig. 20, must be one of the thoracic rings, and fig. 21, 



