FRONTAL SPINE OF HYBODUS. 279 



Lower jaw of the common Hamster. 



I have also drawn one of the rami of the lower jaw of the 

 common hamster, since it exhibits a modification of form 

 which is important, especially to the investigator of fossil 

 remains. 1 The peculiarity in this jaw consists in the ramus 

 being so curved that the angle is considerably raised above 

 the line of the symphysis, this line being drawn backwards 

 from the symphysis menti, and parallel with the crowns of 

 the molar teeth, as represented by the dotted lines in the 

 woodcut. If similar dotted lines be introduced in the figure 

 of the lower jaw of the Mus giganteus, it will be seen that in 

 that animal the lower boundary of the descending ramus is in 

 the same line as the lowest anterior portion of the jaw. In 

 the Arvicoli (which appear to constitute a sub-family of the 

 great group Muridce) the angle of the jaw, as in Cricetus, is 

 considerably raised, but excepting in these animals T am not 

 acquainted with any rodents in which this is the case. 

 (To be continued). 



Art. IV. — Description of the Frontal Spine of a second species of 

 Hybodus ; from the Wealden Clay, Isle of Wight. By William 

 Ogilby, Esq., M.A., F.R.A.S., &c. &c. 



The beautiful fragment of the jaws of Hybodus Delabechei, 

 discovered by Mr. Higgins, and described in the last number 

 of the ' Magazine of Natural History,' whilst it throws a new 

 and valuable light upon the structure and characters of that 

 remarkable genus of extinct fishes, has enabled me to ascer- 

 tain the nature of a small fossil which had been for some time 

 in my possession, but of which neither myself, nor the scien- 

 tific friends to whom I showed it, could imagine the origin or 

 relations. It consists of the tri-furcated base of a cranial 

 spine, (fig. 37), or rather of the middle and one of the lateral 

 processes, the corresponding process of the opposite side 



1 Fossil remains of a species of this group are figured n the ■ Nouveaux 

 Memoires de la Societe Imperiale des Naturalistes de Moscou ; see tome 

 iii. tab. 20, fig. 6. 



