80 BRITISH FOSSILS. 



should tend to show that this " Tilestone " species is the opposite 

 sex of the P. gigas, it will still have been worth while provisionally 

 to separate them. 



Body Joints. The complete specimen, Plate XIV. fig. 1, shows 

 that the body was not greatly elongated, the segments being all 

 rather widely transverse, the seventh, for instance, being fully four 

 and a half times as wide as long ; the eighth and ninth are gradually 

 narrower, but the tenth still shows a width two and a half times 

 greater than the length, while in P. anglicus the corresponding 

 joint appears so have been no more than one and a half times the 

 length (see Plate V. fig. 1). 



The penultimate joint is squareish, or rather inversely conical, not 

 much expanded below. It is about one-fourth wider than long (as 

 in P. anglicus), and this at the hinder part only. A strong central 

 keel runs down its whole length, covered with large squamse, and 

 the margins are similarly ornamented. 



If the caudal joint, Plate IX. fig. 18, be of this species, it has lost 

 the terminal apiculus. It is nearly elliptical, the base truncated- 

 It is fully four inches long. 



The sculpture of the body rings consists of open semicircular 

 squamse, flattened along the anterior border and more convex 

 behind, occupying the anterior half of the segment in the front 

 rings, and more in the hinder ones, till, in the eighth and ninth, 

 they nearly cover the segment. On the sides they are more elon- 

 gate, and, as in other species (P. gigas, for instance, Plate VIII. 

 fig. 5), those on the upper side are more elongate and pointed than 

 those on the lower. All the plicae are prominent and sharp-edged. 

 There are very few intermediate ones, Plate XIV. figs. 2, 11, but the 

 surface of the cuticle is generally roughened between the plicae. 

 Some segments show the plicae very large, fig. 2, and must have 

 been at least fourteen inches broad. Other specimens in the Ludlow 

 Museum show four or five rings overlapping, and some are sub- 

 cylindrical, and with sharp edges. The caudal joint (twelfth) is 

 broad-oval and shortly apiculate, less abruptly so than in P. angli- 

 cus, which, too, has a less regularly oval form, the greatest breadth 

 being below the middle. It is marked all the way down dorsally 

 by a strong carina covered with broad squamse, and the edges are 

 also squamate, in two or three rows. In the specimen from Trimp- 

 ley, fig. 12, the sides are marked by oblique radiating interrupted 

 lines. 



Epistoma and Labrum (not figured). This plate is as large as 

 that of P. anglicus, Plate III., and nearly like in all its parts to it. 



