BRITISH FOSSILS. 23 



turbecl. The palps of the ectognaths are displayed in situ on each 

 side ; the cutting edges of these appendages are seen on each side of 

 the middle line and are turned towards one another, while the large 

 metastoma lies between them, overlapping their respective inner 

 margins. Internally to their serrated edges, a series of articulated 

 teeth (c'), like those connected with the free edge of the basal joint 

 of the organ described above, can be seen upon each side, but the 

 rest of the basal joint cannot be made out. 



On the left-hand side of the head, however, the remains of two 

 palpiform bodies (c), evidently of the same nature as those described- 

 above, and provided with similar strong curved setae, are visible. 

 On the right side is an impression of a similar character, but its 

 minutiae cannot be satisfactorily deciphered. 



The facts I have detailed may be variously interpreted. Either 

 the two palps belong to one basal joint, or there are two basal 

 joints, each with a palp. In the former case there would be one 

 endognath on each side, with a double palp ; in the latter, two 

 endognaths, each with a single palp. As the evidence stands at 

 present, I see no means of arriving at a well-grounded opinion on 

 this subject, and I prefer to abstain from conjecture. 



3. Pterygotus peromatus. The opposite impressions of part of 

 an example of this species are exhibited by two slabs, each of 

 which shows more or less distinctly the carapace and one of the 

 body segments. 



On the larger slab (Plate XV. fig. 2), the impression of the 

 metastoma is distinguishable within the outline of the carapace, 

 but it is thrown out of place, so that its long axis is directed 

 obliquely forwards and to the right side, at an angle of forty-five 

 degrees to that of the body. Close to the anterior extremity of 

 the metastoma, but projecting beyond the boundary of the carapace, 

 lies the basal joint (c) of an appendage with articulated, curved, 

 pointed and striated, teeth, like those of the endognaths of the 

 preceding species. 



The dentated edge of this organ lies almost parallel with the long 

 axis of the metastoma; but beyond it, and more towards the middle 

 line of the body, there is another curved edge (c'), similarly provided 

 with striated and articulated teeth, but cutting the first at a large 

 angle. Is this part of a second endognath of the same side, or is it 

 that of the other side turned round ? In any case the parts are 

 thrown far out of their natural position. 



On the left-hand side, between the base of the metastoma and the 

 middle of the lateral margin of the carapace, the imperfect impression 



