690 



PROP. T. H. HUXLEY OBSERVATIONS 



of the existence of anterior cervical ribs. There is no evidence of 

 the occurrence of intercentral ossifications. 



The abdominal ossicles, so far as they are visible, resemble those of 

 Hyperodapedon and Sphenodon, but no specimen I have seen enables 

 their details to be satisfactorily made out. 



The skull, in its general characters, resembles that of both Hypero- 

 dapedon and of Sphenodon. In contour, it is intermediate between 

 the two, having the occiput relatively somewhat broader than in 

 Sphenodon and much narrower than in Hyperodapedon. 



The anterior nasal aperture is single, as in Hyperodapedon, and 

 the strong recurved premaxillary rostrum has essentially the same 

 structure, and probably was ensheathed in a horny envelope. On 

 the other hand, the dentary edge of the maxilla is but very slightly 

 convex downwards : and, viewed from below, there is a corresponding 

 difference from Hyperodapedon. The outward lateral concavity and 

 inward convexity of the dentary edges of the maxillae are very slight, 

 and consequently there is no such anterior narrowing and posterior 

 widening of the palatal surface as in Hyperodapedon. The palatal 

 bones are not fully exposed in any specimen, but in one there is 

 evidence that they bear certainly not more than two longitudinal 

 rows of teeth, perhaps only a single row ; consequently they are 

 narrow, as in Sphenodon ; and, as in the latter genus, leave the ante- 

 rior portions of the pterygoid bones, which lie between them, un- 

 covered (Plate XXVII. fig. l,pt). The symphysis of the mandible 

 is relatively short, and the rami do not curve outwards as they do in 

 Hyperodapedon. The mandibular rostral processes, between which 

 the premaxillary rostrum is received, are short and obtuse (see 

 fig. 2, p. 682). 



Thus the skull of Rhyncliosaurus resembles that of Hyperoda- 

 pedon and differs from that of Sphenodon, in its single anterior nasal 

 aperture, its premaxillary and mandibular rostral processes, and, 

 perhaps, in possessing more than one series of palatal teeth ; but, 

 in general form, and in the shape of the maxillae, palatal bones, 

 and rami of the mandible, it departs far less from Sphenodon than 

 Hyperodapedon does. In another respect, Rhyncliosaurus appears to 

 differ from both Hyperodapedon and Sphenodon, in that no distinct 

 teeth are discernible on the dentary edges either of the maxillae or of 

 the mandible. Without microscopic examination of sections of the 

 parts, it is impossible to say whether the maxillae and the mandible 

 of Rhyncliosaurus were really edentulous or not. If they were, this 

 genus will present an interesting approximation to the Anomodontia. 



Two other specimens (Xo. 2, and its counterpart, Xo. 3) display 

 the coracoids (co) in place (Plate XXVII. fig. 3). These bones are 

 broad and expanded, 34 millim. long and 20 millim. wide, and 

 have convex median edges. Close to this edge of the right coracoid 

 (in Xo. 2) lies the interclavicle (i.cl.), 30 millim. long. It is 

 narrow, blade-like, and bent dorsad at its anterior end. Here it 

 expands transversely into two arms, which are short, but are not 

 improbably broken. The clavicles are wanting, unless the part 

 marked cl. in fig. 3 represents one. 



In the specimen of Rhyncliosaurus to which I have already referred 



