62 BRITISH FOSSILS. 



transverse, c and d are nearly square, thickened at their ends, 

 which are ornamented by a crest of spiniferous tubercles. Similar 

 tubercles occur scattered over the surface, and particularly on the 

 outer edges and down the middle. They are also in parts orna- 

 mented with minute plicae parallel to their length. It is not quite 

 certain if c and d are single joints, or two styles parallel to one 

 another and pressed closely together, d is probably a pair of joints, 

 as besides the crested spiny edge, it is furnished with a pair of thick 

 curved spines (like those of the succeeding joints) on each half. 

 efgin. the longer filament are of less diameter, successively shorter, 

 but still thickened at their ends, and furnished with thick curved 

 spines three or four in number ; the terminal joint Ti, I, in both fila- 

 ments is a strong simple curved spine, without a striated surface or 

 any serrations to the border. These terminal joints are not well 

 ' seen in the large specimen figured in PlateXI V., but the proximal 

 joints are more perfect. 



The position given to the palpus in this plate, XIII., with the 

 spiny crests directed forwards, is in conformity with the position of 

 the much larger spines in P. punctatus, fig. 9. 



It is difficult to prove the existence of two separate maxillary 

 pieces from any of these specimens (Plate XIII. fig. 2, affording the 

 best evidence on this point). But it seems pretty clear that there 

 were two palpi on each side, one simple, the other branched from 

 near its base : the number of joints before branching cannot be 

 stated with certainty. If only two filaments be admitted on each 

 side, the alternatives will be a single mandible with a branched 

 palpus, or two mandibles each with a simple palpus. We have 



fortunately met lately with a specimen (fig. 7), tolerably perfect,. 

 and showing the basal serrate joint, with six simple joints follow- 

 ing ; the terminal uncinus is lost. There must, therefore, be two 

 jaws, one of which has a simple palp : the other most probably a 

 branched one. 



