96 BRITISH FOSSILS. 



though not carried over a much larger part of the surface, is far 

 more prominent and remote). 



A specimen, crushed longitudinally (fig. 13), shows that the 

 species was rotund in section, as in P. punctatus and others. 



Antennce.^ In all probability Plate XIII. fig. 8, represents the 

 antenna of this species. Its resemblance to those of P. problema- 

 ticus is very close. The shaft is linear, the long end turned abruptly 

 up, and the teeth straight, narrow, and remote, as in that species ; 

 but the chela is much more slender, three inches and a half to four 

 inches long, and the larger central tooth is scarcely longer than the 

 diameter of the shaft itself; while the secondary teeth, some of 

 them at least, approach it more nearly in size. The tooth at the 

 base of the large terminal mucro is appressed against it, and the 

 mucro itself (Plate XI. fig. 3) is sometimes oblique. All the teeth 

 are finely striate, the striae tending obliquely backward on the 

 principal teeth. There are numerous sharp, conical, minute teeth 

 between the secondaries. 



Endognaths (Maxillce .?) Most probably Plate XIII. fig. 15, 

 represents the first or second pair of these organs, and it is pretty 

 clearly referable to P. arcuatus, and not to P. punctatus, which 

 has much shorter and blunter mandibles. (Plate XI. fig. 6.) 

 It is elongate, or even falcate, the upper lobe a greatly convex, the 

 posterior portion (/) drawn out laterally instead of backwards ; the 

 surface closely sculptured all over. The teeth are not oblique, 

 straight, and conical as in P. punctatus, but lanceolate and curved, 

 and directed outwards. About ten or eleven are free, the rest con- 

 fused, either in a horny plate or mixed with setas. In this parti- 

 cular, and in the production of the lower lobe b, it resembles 

 P. punctatus, but the great curvature and elongation of the plate 

 distinguish it. 



Base of Swimming Foot, Plate XL fig. 10. Most probably, from 

 the very convex form of the anterior edge, and the greatly elongate 

 teeth, this belongs rather to the present than to P. punctatus. 

 [Plate XIII. fig. 14, may, perhaps, represent this part in the latter 

 species.] 



Post-oral Plate, Plate XV. fig. 5. Found at Leintwardine, by 

 Mr. Alfred Marston. It differs from the corresponding plate in all 

 the species, having the lobes of the apex narrow, and nearly their 

 own width apart, the sinus between them being very wide and 

 shallow, instead of a simple deep notch. The plate is cordato- 

 lanceolate, for the upper two-thirds it is oval, the greatest width 



