PROF. H. G. SEELEY OTS ARISTOSTJCHTJS PTTSTLLTJS. 225 



though I may think the resemblance strongest with Coslurus and 

 AUosaurus, it may be equally strong with Ceratosaurus. But when 

 Prof. Harsh refers pelvic structures so similar as the pubes of 

 AUosaurus and Ceratosaurus to distinct suborders of the Dinosauria, 

 I can only conclude, if these references are correctly made and 

 sustained, that the pubis is not always a bone on which a generic 

 identification can be based, especially when it is imperfect proxi- 

 mally. I should not thus have ventured to question Prof. Marsh's 

 reference of this pubis to a genus of his own creation were it not 

 that there is what I regard as strong ground for believing that the 

 sacrum associated with the pubis, no less than the dorsal vertebra 

 figured by Sir R. Owen, belong to a genus which can be but 

 distantly related to Coslurus. 



Sir R. Owen, in representing the vertical section of the dorsal 

 vertebra, shows that the centrum is formed of the same kind of 

 tissue, and ossified in the same way as the vertebrae of Dinosaurs 

 in general, except that a fusiform longitudinal space is enclosed 

 which gives no indication of being pneumatic, and appears to open 

 into the neural canal. 2sow, in Coslurus, Prof. Harsh has defined 

 a genus which, in the construction of its axial skeleton, can only be 

 compared to Ornithosaurs, having the bones invested with a thin 

 film of bone-tissue of uniform thickness and distinctive peculiar 

 texture. This character is as well demonstrated in Marsh's section 

 of a dorsal vertebra as in the cervical region. Therefore the dorsal 

 vertebrae of Aristosuchus cannot be referred to Coslurus. Moreover 

 the mode of attachment of the ribs is dissimilar. And hence I 

 submit, as the sacrum of Coslurus is unknown, there is no reason to 

 suppose that it would i>e at all like the sacrum of Aristosuchus, 

 which I now describe. \ 



There are five vertebrae in the sacrum completely anchylosed 

 together by their neural arches (fig. 13), and either anchylosed or in 

 process of anchylosis by their centrums. Sir R. Owen regards the 

 two posterior vertebrae as sacral, and the three anterior vertebrae as 

 lumbar. Here the difference of interpretation must be adjusted by 

 the definition of the sacrum which is adopted. If the sacral vertebrae 

 are those from which strong sacral ribs are given off for support of 

 the ilium, then no doubt only two such vertebrae can be counted, 

 and the other three vertebrae in which the ilium is more or less 

 supported on transverse processes given off from the neural arch 

 may be termed sacro-lumbar vertebrae. This, however, involves 

 theoretical considerations which cannot be demonstrated, for it is 

 impossible to say how many sacral nerves united into a sacral 

 plexus. And as all the transverse processes have the same trans- 

 verse development (fig. 13, t), and the anchylosis of the vertebrae 

 shows that they took part in supporting the body, I adhere to the 

 old nomenclature, and regard all the vertebrae which supported the 

 ilium as sacral. I believe the anterior vertebrae also contributed to 

 support the pelvic bones, though their share in the work was less 

 than that of the last two. 



There is a fundamental difference in the plan of structure of the 



