BRITISH FOSSILS. 61 



masticating organs (exclusive of the serrate bases of the swimming 

 feet) as before indicated for P. perornatus. 



Fig. 1 in Plate XIII. occurs with the fragments of the species, 

 and probably belongs to it, as its form is so elongated or compressed 

 laterally (compared with those figured on Plate VII., which belong 

 to a broad-headed species). The length from the serrate edge a b, 

 to the end of the basal process /, is no greater than the breadth of 

 the serrate margin a b. The general form is broad-falcate, the pro- 

 duced base / squareish, and the insertion of the palpus c very near 

 the serrate margin. This is beset with curved narrow teeth, six or 

 seven of which are distinct in the upper half, and there are numerous 

 smaller ones below. The teeth are articulated with the margin, 

 not mere processes of it, as in the serrate base of the ectognath. 



Figs. 2, 3, 4, however, belong certainly* to P. acuminatus. 

 Fig. 3 shows the endognath a, seen only in part, with a simple 

 palpus attached c d, of which only two joints are preserved ; the 

 lowest c broad and almost urceolate (not shortened, as in Plate VII. 

 fig. 9), and about as long as wide. The second d is narrower; minute 

 plicse cover the base of both joints. Beneath this, and apparently 

 attached to a distinct plate e, pressed closely upon a, and sculp- 

 tured like it, is another and broader palp, of which only the basal 

 joint is visible ; and we must refer to a more perfect specimen 

 (fig. 2, 2 a) for other details of this appendage. 



In fig. 2 the endognath a is seen to have a straight edge above, 

 with which the serrate margin forms an obtuse angle (about 120). 

 It is rather suddenly contracted where the teeth begin ; they are 

 very oblique, narrow, conical, with a rounded base, and straighter 

 than those of the separate specimen, fig. 1 (the latter is, however, 

 as before said, probably the same species). 



The first two joints of the single palpus c d are quite distinct, 

 and c in fig. 2 a shows a toothed distal edge, such as is seen in the 

 joints of fig. 4. The second palpus (probably attached to the crushed 

 second maxillary piece) shows obscurely three or perhaps four 

 broad joints at base, / g, and then divides into a pair of jointed 

 styles h i k I, with tubercular or spinose joints. 



Fig. 4 explains this second appendage, it has a broken and 

 obscure basal portion a (which may be part of the serrate basal 

 joint ?) followed by three broad joints bed, the second (&), being 



* As Prof. Huxley has described Plate XV. fig. 1, in detail, I need only refer to it 

 here (see p. 22.) It shows, I think, the single and branched palpi; but only one 

 mandibular piece, -with teeth, is visible on each side. 



