84 STUDIES ON THE ELASMOBKANCH SKELETON, 



and an anterior, smaller, saddle-shaped, and placed in front of and 

 above the other, from which it is not distinctly separated. This 

 large and prominent articular surface distinguishes the present 

 genus very markedly, though modifications in the same direction 

 are to be observed in the case of Galeus and Scymnus. 



There is no second foramen near that for the glossopharyngeal 

 such as occurs in some genera. The orifice for the facial nerve is 

 situated far forwards, separated by a considerable interval from the 

 articular surface for the hyo-mandibular and near the trigeminal. 



The orbitis covered above by a wide lamellar roof produced behind 

 into a post-orbital process ( Po 0) which is likewise lamelliform, 

 and is curved downwards and backwards ; the latter does not come 

 into direct relation with the palato-quadrate cartilage. In front, 

 the roof bends down towards the base of the skull and bounds the 

 orbit anteriorly, forming a distinct though not prominent prae- 

 orbital process. Below, the orbit is bounded by a cartilaginous 

 lamella which slopes downwards and outwards from the basis 

 cranii. This lamelliform process or basal plate {Ba), is interrupted 

 in front by a deep irregular incision, and behind there is a large oval 

 foramen. 



On comparing the skull of Carcharodon with a dried skull of 

 Lamna cornubica, I can find little difference between the two. In 

 both are the same postero-lateral processes for the articulation of 

 the hyo-mandibular ; in both the auditory foramina lie in a groove 

 which runs along a broad central ridge ; in both thin lamellae of 

 cartilage overarch the orbits ; and both have the same form of 

 three-barred rostrum. As, however, the structure of the skull in 

 the family to which both these genera belong has never been 

 described, I have entered with some minuteness into the above 

 description. 



The palato-quadrate is suspended, as in most Plagios tomes, by 

 means of a hyo-mandibular, which is lai-ge and articulates with 

 skull by a broad articular surface. Attached to the hyo-mandi- 

 bular and hyoidean cartilages are about twenty irregular rays, with 



