22 BRITISH FOSSILS. 



edge. These teeth, however, do not form one even series, either 

 as 'regards their size or their position. They commence large, near 

 to what I will term the anterior margin of the plate, but not 

 close to it, the antero-lateral angle being rounded off and 

 oiving rise to no tooth. In this respect it represents the corre- 

 spondincr part of the endognath of P. punctatus just described. 

 After four or five large ones, the teeth rapidly diminish in size and 

 become indistinguishable. The free edge of the plate then makes a 

 slight curve, so that it projects beyond its former line and then gives 

 rise to two teeth of the same size as the most anterior ones, after 

 which it becomes lost beneath the matrix. A depression runs from 

 the commencement of this projecting edge into the crushed and 

 transversely folded, middle part of the plate. In front of this 

 crushed portion, the anterior region of the plate is, in its outer half, 

 richly sculptured ; behind and internally, the substance of the organ 

 is for the most part broken away, but shows the remains of a 

 similar sculpture outside the broken edge. The opposite half of 

 the specimen exhibits the impression of the sculpture over this 

 broken part, but in neither half can the ornamentation be satisfac- 

 torily traced continuously over the middle crushed region. 



The outer part of the joint, just described, is continued into a broad 

 mass, so divided into two portions externally, as to appear like two 

 palps. Each palp-like division appears to possess at least three 

 joints, and the distal margins of the outer of these joints in the 

 anterior " palp " are produced into strong curved processes or seta3. 

 . The part represented in Plate XIII. fig. 4, apparently consists of 

 these palpiform appendages detached from their basal joint. Four 

 or five gradually tapering joints are here distinguishable, and each 

 is produced into setaB along it distal edges, while the terminal 

 articulation resembles a curved claw. 



The same kind of basal plate, apparently provided with similar 

 appendages, is shown in another specimen (Plate XIII. fig. 3), but 

 the parts are here overlapped by the broken ectognath, and are so 

 crushed and confused that I can arrive at no satisfactory conclusion 

 regarding them. 



A valuable example of P. acuminatus from Lesmahago 

 (Plate XV. fig. 1), although greatly crushed, and at first sight very 

 unpromising, yields a great deal of valuable information on patient 

 investigation, and shows, among other things, that the organs under 

 discussion belong to the mouth and to the endognathary series. In 

 fact, in both halves of this specimen, the ectognath and the meta- 

 stoma are very clearly traceable, and are evidently almost undis- 



