18 



BRITISH FOSSILS. 



jugular plates (G). The surface of each of these bones ex- 

 hibits a very peculiar ornamentation, consisting of delicate undu- 

 lating ridges, which, on the whole, run more or less parallel with the 

 outer edges of the jugular plate, but, in front, converge towards its 

 inner edge. The peculiar form and sculpture of the rami of 

 the mandible, are better displayed by other specimens. In front 

 of their symphysis there is a confused mass, doubtless formed 

 chiefly by the premaxillse, and which exhibits indications of small 

 teeth. 



The broad ends of the pectoral arches are displayed at b ; but 

 the pectoral fins are not visible. 



The large, obtusely lobate, ventral is well shown at V. It has, at 

 present, fourteen fin rays, which gradually increase in length on 

 either side towards the middle four, which are about equ^l. These 

 rays present no sculpture, but the broad jointing of their distal 

 halves is very well displayed. 



The remains of the dorsal fin appear at D. 



The caudal fin has about ten fin rays above and below, which 

 are connected with the neural spines by interspinous bones. The 

 rays are jointed in their distal moieties ; and the hindermost ones 

 are shorter than the others, and lie more nearly parallel with the 

 axis of the body. The latter narrows rapidly from the commence- 

 ment of the caudal fin, and continues scaly to its truncated and 

 evidently broken extremity. 



The scales «, fig. la, have the same form and sculpture as in the 

 preceding specimen. Fig. 1^. exhibits a magnified view of the 

 ornamentation of part of one of the jugular plates. 



No. 3. The specimen represented in PL III., fig, 2. 



The chief interest of this specimen (figured of twice the natural 

 size) arises from its .showing at h the crushed walls of the ossified 

 air bladder, and, at a, what appears to be the interspinous bone of 

 the posterior dorsal fin. Its crura diverge at a somewhat more 

 open angle than that shown in the figure. The anterior dorsal fiii 

 (Z)) of this specimen is unusually long. 



No. 4. Tlie specimen represented in PL III,, figs. 3, 3a, and PI, IV., 



figs. 1 and 2. 



Of these figures the first is of the natural size ; the two others 

 are magnified, and fig. 2, Plate IV,, has been accidentally inverted. 

 They are taken from the two counterparts of a split specimen, and 

 throw much light upon the structure of the mandible, the jugular 

 plates, and the branchial apparatus. 



Each ramus of the mandible (Mn), when viewed laterally, as in 

 fig. 2, Plate IV. (which represents the right ramus) presents a nearly 

 straight lower margin, while the upper edge is sinuous ; the upper 

 contour of the ramus attaining its greatest height rather behind its 

 centre, and thence rapidly descending forwards and backwards. In 

 the horizontal plane, the hinder part of each ramus is nearly 

 straight, but its anterior end curves sharply inwards towards that 

 of its fellow (Plate IV., fig. 1), to the symphysis. 



