2 



BRITISH FOSSILS. 



expanded towards the occiput, and bearing two remarkable promi- 

 nences behind the orbits. Behind and beneath this projection, on 

 the right side, is seen a strong process extending downwards and 

 backwards (fig. 8). This, from its form and position, must be 

 the mastoid bone ; although, from the obliteration of all sutures, it 

 is impossible to determine whether it is not partially composed of 

 the postfrontal. Immediately in advance of the frontal bones are two 

 small semilunar bones (fig. 15) corresponding to two semicircular 

 emarginations of the anterior edge of the frontal plate, and two 

 recessed facets of the premaxillary bone (fig. 22). With respect to 

 these bones. Professor Owen writes as follows : — " I am now satis- 

 fied, from the way in which the bones or divided bone fit into the 

 emarginations of the frontal, that they are the nasals, answering to 

 the similarly divided but more elongated nasal of Lepidosteus." In 

 following up this view the correctness of the identification becomes 

 evident on examining the corresponding parts in the genera Poly- 

 pterus and J. mm, where we find the long narrow nasals of Lepidosteus 

 represented by bones very similar in form to those of the fossil 

 under consideration. External to these bones are two small ossicles 

 (fig. 19), occupying the position of the "nasaux'' of Cuvier. These 

 are the turbinals of Owen, and correspond closely with these bones 

 in the recent Amia calva. Several fragments of bone (fig. 73) occur 

 between the turbinals and the upper maxillary, apparently belong- 

 ing to a large lachrymal or suborbital bone. Immediately behind 

 the upper portion of this bone a recess in the frontal bone marks the 

 position of the orbit, and attests the absence of the supraorbitals 

 which surround the orbit in Lepidosteus. The area of exposed chalk 

 between the orbit and the preoperculum may have been occupied by 

 a large postorbital plate, as in Arapainia and Amia. The upper jaw 

 is composed of a single cuneiform premaxillary and of large arcuate 

 maxillary bones, as in Arapaima (Plates x., x*, figs. 21, 22). Each 

 of these components supports a single row of long, sharp, conical 

 teeth, very regular in size, incurved at the points, and fluted on the 

 surface. Within there is a second row of similar teeth, but rather 

 smaller in size ; the central ones are situate on the vomer (Plate x., 

 fig. 18), and the lateral ones on the palatine bones (Plate x., fig. 20). 

 The lower jaw is composed of long and broad dentary bones (Plates 

 X., X*, fig. 32), with small articular ossicles (fig. 30) at the con- 

 dyloid extremities. The teeth are of like character with those of the 

 upper jaw, and equally regular, but they are implanted in a double 

 row ; those constituting the outer row being considerably larger than 

 the secondary ones. The operculum (Plate x*, fig. 35) is of moderate 



