84 BRITISH FOSSILS. 



the tail joint or telson appears to be emarginate instead of pointed. 

 But if this character should be deceptive, there can be no doubt of 

 the specific difference, since this joint is furnished with a most re- 

 markable elevated crest or ridge nearly half an inch high, which is 

 quite absent in the Scotch species. 



As the fragments indicate a species of the largest size, the above 

 specific name will not be inappropriate. The size of the chelate 

 antennae exceeds that of any known species. 



There are two species in the Kington beds, P. gigas and P. pro- 

 blcmaticus, and it was of course possible that some of the parts, 

 assigned to the former might belong to the latter species. The 

 subsequent discovery of nearly all the parts of P. problematicus 

 shows that in this instance the fragments have been rightly 

 collocated. 



Head or Carapace, Plate VIII. fig. 1. Nearly semioval, convex, 

 the width three inches and three quarters at the broad base, probably 

 greater than the length. The specimen being imperfect behind, the 

 true length is not known, but the portion preserved is three inches 

 and a quarter long. The eyes are very large, three quarters of an 

 inch long, oval and prominent beyond the margin. They are placed 

 very near the anterior end, and the space between them on the 

 margin is about an inch and three quarters, while between the 

 convex inner edges of the eyes it is about an inch and a half. The 

 anterior border is arched and very slightly angular in front, with a 

 crenulate edge. The sides are convex (their margin not visible). 



In the centre of the carapace, and forming an equilateral triangle 

 with the eyes, is an elongate tubercle. The general surface appears 

 somewhat rugose. 



Epistoma, fig. 2. The proportions of this plate and its sculpture 

 are very like those of P. anglicus ; and the specimen figured indi- 

 cates this part to be quite as large as that in Plate III. fig. 7. 

 The plicae on the upper or front portion (a) are crowded, and 

 but slightly curved ; those further back are semicircular or even 

 semioval, while those near the apex of the side lobes are narrower 

 and pointed as in the cognate species. Similar but smaller plicae 

 occur down the centre lobe, which does not appear to have promi- 

 nent elongate scales, nor is it convex as it is in P. anglicus. Its 

 base c is broad and spear-shaped. 



Body Rings. The anterior body rings, fig. 3, bear the squamae 

 only on their front half, and these are less curved and less crowded 

 than in the corresponding segments of P. anglicus. The edge of 

 the plicae is thickened. Figs 4 and o must represent large segments 



