42 BRITISH FOSSILS. 



Endognaths (Mandibles, &c.} The under side of the carapace, of 

 which fig. 4. is the cast, shows the great foliaceous bases (with serrate 

 inner lobes) of the swimming feet (c). No mandibles or maxillse* 

 have been discovered beneath these ; but in fig. 1, at c, the long- 

 filiform palpi of one pair of these organs extend right and left 

 of the carapace. They are more elongate than in other species. 



A small mandible, found since the plate was engraved, is here 

 oiven as a woodcut. It is contracted in width as compared with 



|pi|||iy ^%, r p, the basal or attached portion ; 

 Endognath (Mandible), natural Z, HP ^ ? 



size ? of Pterygotus bilobus. ^ - C ~ 3 ' pa 



the shape in some other species. The anterior serrate lobe a is 

 narrow, and with sharp curved articulated teeth. The lamina p is 

 oblique and sub-triangular ; and the palpus, set on rather far back 

 from the serrate border, has a small quadrate basal lobe c followed 

 by a longer one d; the third and fourth (ef) are linear, and 

 several times as long as broad. The terminal joints are still 

 longer, as seen in Plate I. fig. 1 c (compare this with Plate VII. 

 figs. 4, 5.) 



Epistoma and Labrum. Of the large semicircular piece which lies 

 in front of fig. 1, and which has evidently been shifted from the under 

 side of the head, we can only judge the true position by comparing 

 it with other species (H. perornatus, for instance, fig. 16, in which 

 the mid-lobe a of the organ is seen to be of an ovate shape) ; 

 also in Plate XV. fig. 2 /, where a similar piece lies in front of 

 the head. 



In fig. 1 the semicircular outline probably corresponds to the 

 hinder free margin (of much more angular shape) in the epistoma of 

 P. anglicus, Plate III. The mid lobe a is obscurely marked out, 

 but is of an ovate shape ; its insertion not very clearly seen. 



Ectognaths. Fig. 3 shows these organs in their place at the 

 lower angle of the carapace, drawn forward as for a stroke ; the 

 forward bend of the limb at the fifth joint ca, and the great serrate 

 bases b indistinctly visible through the crust. Fig. 9, with part of 

 the carapace broken away, has both lirnbs in place, and figs. 1 and 2 

 show these natatorial feet laid backward close along the body. 



* The dilated bases of the swimming feet (ectognaths) -were formerly supposed 

 to be the mandibles, and the produced neck-like portion to be jointed ; Quart. Journ. 

 Geol. Soc. 1. c. This has been set right by Professor Huxley (see Part I.) 



