624 PROF. H. G. SEELEY ON [Aug. I9OO, 



preserved. The teeth are certainly in distinct sockets : they are 

 placed obliquely in the jaw, so that their anterior margins are 

 inclined towards its inner side. The crowns are sharp-pointed, and 

 moderately prominent, compressed laterally, with sharp lateral 

 ridges, which appear to be serrated. The crowns are inclined inward. 

 A small pulp-cavity descending into the socket is seen in the root of 

 one tooth. In another tooth the smooth enamel appears to show the 

 delicate transverse lines of growth. 



The coronoid element appears to be somewhat elevated, rising 

 behind the teeth on the inner side of the jaw. 



The Vertebral Column. 



Prof. Wiedersheim counted thirty-four to thirty-six vertebrae,, 

 grouped as twenty-one or twenty-two pre-sacral, two or three sacral, 

 and ten to twelve caudal. There appear to me to be twenty-two or 

 twenty-three in advance of the pubis,, four or five in the ischio- 

 pubic region, and about nine of the caudal vertebras are behind the 

 pelvis, so that. I count a total of thirty-six vertebras. 



The neck, owing to the forward positiou of the shoulder-girdle, is 

 obscurely defined. There is no evidence of ribs in the earliest 

 vertebras. 



On the right side there are sixteen pre-pelvie ribs preserved, all 

 of which have the characters of dorsal ribs. This would appear to 

 limit the cervical vertebras to seven. 



It is probable that the sacral vertebras did not exeeed three in 

 Aristodesmus. Hence the vertebral formula may read as seven 

 cervical, sixteen dorsal, three sacral, and ten caudal. 



The centra are so exposed as to show their deeply biconcave 

 articular ends, with the cups penetrating much as in Anthodon and 

 JHcsosaurus, so as to be only slightly separated one from the other in 

 the middle of the centrum by a narrow partition of bony substance. 

 The only centrum in the dorsal region from which the form can be 

 obtained perfect, is on the ventral border as compared with the 

 neural border of the relative length of 2 : 5. 



This may suggest that the back was unusually convex ; the same 

 effect would result from intervertebral elements on theventral border. 

 Hence as the vertebras all lie in the same plane, their visceral arti- 

 cular borders are well separated one from the other. The anterior 

 face of the centrum is larger than the posterior face. The form is 

 subtriangular, with the external margin thickened and rounded. 

 The lower half of the posterior articular face appears to make an 

 angle with its upper part : I can only interpret the angle as due 

 to an intercentrum. 



The sides of the centra are concave from front to back,, and 

 their surfaces converge interiorly with a somewhat pinched aspect, 

 so as to form a narrow rounded base to the centrum. 



The transverse processes to which the ribs are attached, given 

 off from the sides of the centrum, are strong, and placed high up, 

 though not reaching the anterior articular face. These processes are 



