PROTOSPHYILENA. 149 



longer and narrower than those of the vomer, and they generally slope forwards, 

 though their direction is a little irregular. The maxilla (figs, 4, 5) is also 

 incompletely known, but it has the form of a stout, narrow bar, with a flattened 

 outer face, which is either rugose or tuberculated (fig. 5). Antero-internally it is 

 produced into a large and stout process (figs. 4, 4a, p.). The oral border bears a 

 close series of teeth in sockets, which are usually oval in section, often with the 

 long axis oblique. The teeth diminish a little at each end of the series, but are 

 otherwise nearly uniform in size, all small compared with those of the premaxilla. 

 Their direction is either vertical or slightly inclined backwards. 



Portions of the dentary bone, especially its anterior end, are associated with 

 the rostrum shown in PI. XXXI, fig. 1, d. The nearly complete mandible, of 

 which the left ramus is shown in PI. XXXI, fig. G, is also directly associated with 

 a typical rostrum. These specimens therefore prove that the anterior portion of a 

 similar mandible figured by Dixon (op. cit., pi. xxxi, fig. 12) and on PI. XXXII, 

 fig. 1, belongs to P. ferox. For the greater part of its length, the dentary bone (d) 

 is a thin lamina somewhat bent on its long axis so that its outer face is convex, 

 and slightly thickened at its upper border to form a ledge for the insertion of the 

 teeth. Its outer face exhibits a fibrous texture, covered with some rugosity 

 which becomes conspicuous towards the symphysis. The bone decreases in depth 

 forwards to a point shortly behind the anterior extremity, and then expands again 

 into a rounded end for the insertion of three large teeth where it meets its fellow 

 in the tumid symphysis. These large teeth (PI. XXXI, fig. 1, and PI. XXXII, 

 fig. 1) are the longest of any in the mouth, and project forwards from the rounded 

 end of the dentary bone. They are fixed in deep sockets, and these are connected 

 on their inner side with a groove in which the successional teeth develop (PI. XXXII, 

 figs. 1 a, 1 b). Immediately behind the large front teeth the constricted part of 

 the dentary bone is toothless. Then follows a single regular series of com- 

 paratively small teeth, which diminish in size towards each end. On the inner 

 face of the anterior end of the dentary there is a separate splenial element (spl.) 

 which also enters the mandibular symphysis. It is thickest in front, tapers to a 

 slender point behind, and suddenly deepens at its middle part to accommodate 

 two large teeth which are implanted here. The large teeth are directed vertically 

 or slightly backwards ; a row of three or four diminutive teeth occurs in front of 

 them, but the bone is toothless behind. This splenial element does not extend for 

 more than half the length of the dentary ; but behind it there must have been a 

 posterior splenial in the form of a thin plate, tapering forwards and upwards, and 

 covered with minute tubercular teeth. This bone is known in certain American 

 species ; and apparently one example of it from the zone of Holaster subglobosits 

 at Amberley, near Arundel, occurs in the Capron Collection (B. M. no. 49827), 

 though the specimen is unfortunately isolated. 



The teeth (PI. XXXI, figs. 7, 8) are solid, bilaterally symmetrical, and com- 



