J50 REPORT 1841, 



in TJwrictes and other lizards : the opercular element extends further upon 

 the outside of the jaw from its lower margin than in the existing lizards ; the 

 Thorict.es again, in this respect, coming nearest to the Rhynchosaurus : the 

 dentary element constitutes the rest of the outer part of the ramus, but not 

 the slightest trace of teeth is discernible. 



The present singular and highly interesting cranium seems to have been 

 preserved with the mouth in the naturally closed state, and the upper and 

 lower jaws are in close contact. In this state we must suppose that they were 

 originally buried in the sandy matrix which afterwards hardened around them; 

 and since lizards, owing to the unlimited reproduction of their teeth, do not 

 become edentulous by age, we must conclude that the state in which the 

 Rhynchosaurus was buried, with its lower jaw in undisturbed articulation with 

 the head, accorded with its natural condition, while living, so far as the less 

 perishable hard parts of its masticatory organs were concerned. Neverthe- 

 less, since a view of the inner side of the alveolar border of the jaws has not 

 been obtained, we cannot be assured of the actual edentulous character of 

 this very singular Saurian ; for in the genera Agama and Chameleo the den- 

 tal system, seen only from the outside of the jaws, is represented by mere den- 

 tations of the alveolar border, and the anchylosed bases of the teeth, the crowns 

 of which really form the dentations, are recognizable only by an inside view. 

 The indications of the dental system are at any rate more obscure in the 

 Rhynchosaurus than in any existing Lacertian ; the dentations of the upper 

 jaw are absolutely feebler than in the Chameleon, and no trace of them can 

 be detected in the lower jaw, where they are strongest in the Chameleon. 

 The absence of the coronoid process in the Rhynchosaurits, which is conspi- 

 cuously developed in all existing lizards, corresponds with the unarmed con- 

 dition of the jaw, and the resemblance of the Rhynchosaurus in this respect 

 to the Tesludo ( Chelys) ferox, would seem to indicate that the correspond- 

 ence extended to the toothless condition of the jaws. The resemblance of 

 the mouth to the compressed beak of certain sea-birds, the bending down of 

 the curved and elongated intermaxillaries, so as to be opposed to the deep 

 symphysial extremity of the lower jaw, are further indications that the ancient 

 Rhynchosaur may have had its jaws encased by a bony sheath, as in birds 

 and turtles. 



A small flattened triangular plate, which adhered to the posterior part of 

 the skull, was suspected by Dr. Ward to be a tooth ; it appeared to me, from 

 the character of the exposed surface, to have at least equal claims to be re- 

 garded as a dermal scute. In prepai'ing the mould of the cranium this part 

 was detached and lost, a circumstance M'hich I have much regretted, since it 

 prevented my applying to it the test of a microscopical examination. 



I proceed now briefly to notice the other portions of the skeleton, which, 

 from their size, texture, and community of stratum and locality, are with much 

 probability referable to the Rhynchosaurus. 



Considerable portions of two rami of two distinct lower jaws, in portions of 

 sandstone from the Grinsill quarries, show the same structure as that of the 

 jaw in the cranium above described ; the thick edentulous alveolar border is 

 bounded below on the outside by the longitudinal channel ; the lower border 

 of the ramus is thick and smoothly rounded, it is somewhat abruptly con- 

 stricted immediately behind the deflected extremity or symphysis. The struc- 

 ture of the bone is very compact ; the fractured end demonstrates the large 

 cavity, common in reptiles, which is included between the opercular and 

 dentary pieces. 



One piece of fine-grained sandstone contains a considerable proportion of 

 four of the dorsal vertebrae in a connected chain, which measures 1 inch 10 



