on the Fossil Genera IchtJiT/osaurus and Plesiosaurus. 121 



The suture dividing- the coronoid bone (.v) and the angular (y) may be 

 traced in the posterior part of the jaw. The coronoid process is not visible. 



Tlie articular bone (3/) seems considerably more developed than in the 

 ichthyosaurus and crocodile, and to approximate more nearly to the corre- 

 sponding part in the proper lacertian type. 



The lower jaw further agrees with the lacertian type, in the absence of the 

 oval hole which characterizes the recent species of crocodiles. 



Upper jaiD, and sutures of the head. — It is very difficult, from the crushed 

 state of the specimen, to ascertain the exact situation of the sutures dividing 

 the component bones of the head. The intermaxillaries {a) appear to occupy 

 a considerable space in front of the nostrils ; the maxillaries (h) to exhibit 

 only a small portion exteriorly. The nostrils are small, and placed as in 

 ichthyosaurus; the sutures dividing the nasal (A), lachrymal {i) and frontal bones 

 (Hhli) are indistinguishable ; and the outline of the orbit has been entirely 

 distorted by the compression the specimen has undergone. The jugal bone (c) 

 is tolerably distinct, and the suture dividing it from the posterior frontal (h') 

 may be traced ; the branches of the parietal (m), and the temporal (n) sur- 

 rounding the temporal fossae, are sufficiently clear. The structure of all these 

 parts closely agrees with that of the lizard, iguana, &c. The os quadratum (0) 

 is suspended as it were by its articulation to the temporal (n), as in the above 

 genera, and not solidly fixed by an insertion among all the neighbouring 

 bones as in the crocodile, and probably in the ichthyosaurus. 



Traces of the occipital and sphenoidal bones may be seen, but in a state so 

 much mutilated and distorted, that it is absolutely impossible to form any judge- 

 ment concerning these parts. Within the left temporal fossa part of a slender 

 cylindrical bone may be observed, which is probably a fragment of the long 

 columnar process uniting the sphenoid to the parietal ; a structure peculiarly 

 characteristic of the lacertian type. The palatal and pterygoidal bones are very 

 obscurely shown; we have only ventured to indicate these parts by dotted lines. 



The accompanying Plate represents. 



Fig. 1. A view of the specimen, placed so as to rest on its upper surface : 

 this exhibits the whole of the right lower jaw, and the jugal and temporal 

 bones and os quadratum of the same side. 



Fig. 2. A view of the specimen, placed so as to rest on the lower jaw, and 

 thus exhibiting all the upper part of the head. 



Fig. 3. A single tooth, rather magnified, and split, so as to show the interior 

 cavity. 



Fig. 4. An attempted restoration of the head, to assist the eye in tracing the 

 connexion of its parts : A. viewed on the side ; B. viewed from above. The 



VOL. VI. R 



