THE KEl) AND NORWICH CRAGS. 



449 



I 



that seen in M. medilineatiis. Indications of this mode of ossifica- 

 tion are also seen in examples of other species of this genus. 



On each side of the mesethmoid there is a distinct channel, 

 running along the upper surface of the rostrum, for about 190 mm. ; 

 it then gives off a much smaller channel, which, passing inwards, 

 follows the tapering point of the mesethmoid, to end with its 

 fellow of the opposite side in the median groove already noticed. 

 Passing forward from the origin of the smaller channel, the outer 

 wall of the larger channel becomes stronger, forming a distinct 

 angle, which continues to the front of the rostrum, and gives it the 

 characteristic flattened aspect, while the channel itself gradually 

 dies out. Towards the hinder part of the specimen the maxillary 

 region on each side is produced into an obtuse lateral angle (fig. A), 

 which gradually subsides as it passes forwards and downwards 

 (fig. E). At about 150 mm. from the front a channel takes the 

 place of the ridge (fig. 7 c), and passes quite to the lower surface of 

 the specimen. A little above and in front of this point, a much 

 larger channel is seen issuing from under the bone and extending 

 to the front of the rostrum ; and below it there is a roughened 

 area from which the anterior extension of the maxillary has been 

 broken away. In the present condition of the specimen the front 

 of the rostrum is formed solely by the two premaxillae, which, 

 although in contact with each other, are distinctly separated by a 

 fissure clearly seen on the upper and under surfaces ; moreover, the 

 line of division is clearly shown on the surfaces where the snout 

 has been broken across (figs. B, C). The boundary separating the 

 maxilla from the premaxilla is seen on the upper surface towards 

 the hinder end (fig. 7 cr) as well as in front (fig. 7 c); but in the 

 intermediate region no such boundary can be traced. 



The openings of the premaxillary canals are on the u})per surface 

 (fig. 7 a) near the posterior extremity of those bones ; and in a 

 hinder view of the specimen the apertures of two other large 

 canals may be seen on each side. 



Near the middle of the rounded lower surface (fig. 7 b) there is a 

 lenticular area, which is probably an exposure of the vomer, and on 

 each side of it is the opening of a canal ; while towards its front 

 part may be seen the sutures separating the maxilla) from the 

 premaxillae. 



The end of a rostrum figured by Van Beneden and Gervais* as 

 ZvphiojJsis servatuis, l)u Bus, bears some resemblance to Mr. Can- 

 ham's specimen in the flattening of its upper surface ; but the 

 narrowing of the hinder part of this region is an indication of 

 important structural differences. Moreover, Zipluopsls or Clionezi- 

 phius, with which it is now included, has the mesethmoid more or 

 less unossified, and not appearing on the upper surface of the 

 rostrum. 



None of the specimens of Mesoplodon, either recent or fossil, so 

 far as I can ascertain, present the same peculiar conformation of 



* Ostt'Ogr. CutaCL's, pi. xxxvii. bis, fig. 8. 



