L. C. MIALL ON THE STRUCTURE OP THE SKULL OF RHIZODUS. 625 



Skull of Rhizodus (-j* - nat. size). 

 JEth 



cations cannot be clearly defined, with the exception of the oper- 

 cular bone. This is distinctly visible on the right side of the skull ; 

 it projects backwards about an inch beyond the general occipital 

 margin. Internal to this is an ossification, most of which is covered 

 by the usual sculpture, though a small tract along the posterior 

 border is nearly smooth. This is, in all probability, the epiotic. 

 Owing to the longitudinal fracture above mentioned, the supra- 

 occipital cannot be defined. In the lower jaw an angular, an arti- 

 cular, and a dentary piece seem to be distinguishable. The articular 

 end is obscure. Displacement upwards has removed or concealed the 

 internal parapet of the alveolar grove, which is not apparent in either 

 ramus. Adjacent to the operculum of the right side is a large 

 crushed bony plate, which exhibits its smooth internal surface. 

 This is detached from its natural position ; and its form cannot be 

 accurately defined. It may belong to the pectoral limb. Behind 



2t2 



