74 BRITISH FOSSILS. 



Endognatks, Plate VII. figs. 4 to 7. There are five or six specimens 

 in the Scotch collections more perfect than that figured by Agassiz 

 (middle left-hand figure), and of larger size, fully four inches and a half 

 long. The palpus, c d e, was probably five or six inches in length, 

 and of considerable thickness. Some fragments even indicate a still 

 larger size for the jaw. 



The mandible is of an oblong form, the front and back margins 

 nearly parallel. The serrate termination of the lamina scarcely at 

 ail expanded into a lobe, and the posterior or basal portion (p) 

 which occupies nearly half the entire length is produced obliquely 

 backwards at a wide angle. This portion is straight in front and 

 only slightly sinuous along the hinder edge, which shows traces here 

 and there of striae perpendicular to the edge, probably due to the 

 insertion of muscular fibres. 



The serrate edge is nearly straight and very oblique forming an 

 angle of about 120 with the front margin. There are about twelve 

 strong teeth, of which the upper six or seven are free, lanceolate, 

 curved, and dilated below, with a constriction as if articulated, and 

 the remainder are connected so as to form ridges upon a thin plate. 

 Minute intermediate ridges occur between these. The posterior 

 angle of the serrate edge is produced a little into a small lobe b, 

 covered with deep punctures as if for the insertion of stiff hairs or 

 setse. The upper edge is not at all expanded or overhanging as in 

 P. acuminatus, the teeth starting at once from the upper angle in 

 a line continuous with the front margin (this is not the case with 

 fig. 7, in which there is an overhanging lobe). 



The general surface of the mandible is covered with obscure plicse, 

 which become distinct and large along the front margin, which is 

 thickened ; the rest of the lamina is rather flat, the base is thin and 

 almost membranous at the edge. 



The palpus is long and stout, directed straight outwards, and 

 consisting of at least five, and probably more joints, of which the 

 basal one (c) is more than twice as wide as long. The next (cZ) 

 unceolate and thickened at the distal end, rather longer than wide. 

 The third takes an elongate form, but is still broad, and its end 

 thickened and somewhat bilobed (e). The next (/) is still longer 

 in proportion, swelled, and a little crenulate or spiny at the tip 

 (compare with Plate IX. fig. 7.) We have no more joints, but 

 in Agassiz's figure the succeeding joint, the fifth, is clearly shown. 



The surfaces of all these joints are covered with transverse plicae. 



Maxilla ? fig. 7. It is probable that fig. 7 indicates a second pair 

 of endognaths, since the proportions of the plate are so different, 

 fig. 7 being considerably longer before the insertion -of the palpu 



