44 



BRITISH FOSSILS. 



visible. Posteriorly, it is broad and expanded, furnishing the con- 

 dyle to the mandibles by its outer and lower margin, while its 

 upper and inner part probably abutted against the sphenoid. An- 

 teriorly, it rapidly narrows, and is continued forwards as a strong 

 bony bar. Running parallel with and outside this, is a second elon- 

 gated bony ridge, which may be distinct from the foregoing, or may 

 be only the outer part of it. At any rate, the two seem to become 

 one in front. Here they support a very strong tooth, and there is 

 a second large tooth situated far back upon the outer bone. 



This palato-quadrate apparatus, taken altogether, very much 

 resembles that of Lepidosteus in form, and in the large teeth which 

 it bears. 



The contour of the stout mandible follows that of the head, 

 the gape extending as far back as the level of the posterior edges 

 of the parietal bones. The rami are very stout, but appear to 

 have consisted of only a thin osseous shell, sculptured externally in 

 the same way as the cranial bones. The constituent elements of 

 the mandible are not distinctly separated from one another in any 

 specimen. 



The jugular plates consist of two principal and a number of 

 lateral scale-like bones. The former are elongated, nearl}^ right- 

 angled, triangles, with their perpendiculars turned towards one 

 another, and their apices engaged in the re-entering angle of the 

 rami, while their bases are situated midway between the articular 

 ends of the rami and the posterior margins of the ojDercular appa- 

 ratus. The peculiar sculpturing of these plates gave rise to the 

 name of the genus, and is well shown in fig. Ic, Plate II. The 

 outer edges of the principal jugular bones lie close to the inner 

 edges of the rami of the mandible anteriorly, but posteriorly a space 

 is left between them, which gradually widens posteriorly, and is 

 so continued between the suboperculum and the posterior part of 

 the principal jugular plate. This interval is filled up by the secon- 

 dary jugular plates, of which, in one specimen, I count five, gradually 

 increasing in size from before backwards. All these plates exhibit 

 the characteristic surface ornamentation, and the last, much larger 

 than any of the others, extends beyond the level of the posterior 

 margin of the principal jugular plate, its curved free margin sweep- 

 ing backwards and outwards, and lying between the suboperculum 

 and the pectoral arch, while a considerable portion of the bone seems 

 to pass under and be overlapped by the suboperculum. There is no 

 median rhomboidal intercalary bone between the anterior and inner 

 edges of the principal jugular bones. 



