Geological Society: — Annivasary of 1839. 229 



legists recognize siicli distinctions as were in this case in qucstionj 

 have been put fully in possession of the rules and the leading 

 examples which apply to such cases. And hence it will not I 

 trust he deemed presumptuous, if, without pretending to any 

 power of deciding a question of zoology, I venture to state the 

 result of these discussions. It appears^ then, that some of the 

 marks by which the under jaws of Mammals are distinguished 

 from tliose of Saurians are the following : (1) a convex condyle ; 

 (2) a broad and generally elevated coronoid process, (3) risiug 

 near the condyle ; (4) the jaw in one piece ; (5) the teeth multi- 

 cuspid, and (6) of varied forms, (7) with double fangs, (8) in- 

 serted in distinct sockets, but (9) loose and not anchylosed with 

 the jaw. In all these respects the Saurians differ; having, for 

 instance, instead of a simple jaw, one composed of six bones 

 with peculiar forms and relations, and marked by Cuvier with 

 distinct names ; having the teeth with an expanded and simple 

 fangj or anchylosed in a groove, and so on. Of course, it will 

 be supposed, by any one acquainted with the usual character of 

 natural groups, that this line of distinction will not be quite sharp 

 and unbroken, but that there will be apparent transgressions of 

 the rule, while yet the unity of the group is indubitable. Thus 

 the Indian Monitor and the Iguana, though Saurians, violate the 

 second chmdiCieVy having an elevated coronoid process; but then 

 it is narrow, and this seeming defect in our second character is 

 further remedied by the third; for in those Saurians there is a 

 depressed space between the condyle and the coronoid process 

 quite different from that which a mammal jaw exhibits. Again, 

 the teeth of Crocodiles, Plesiosaurus, and the like, are inserted in 

 distinct sockets ; but then they have not double fangs. The 

 Basilosaurus was supix)sed to be a saurian with double fanged 

 teeth, but that exception was disposed of afterwards. And as 

 there are thus saurians which trench upon the characters of mam- 

 mals, there are mammals in which some of the above characters 

 are wanting : thus the condyle is slightly or not at all convex in 

 the Ruminantia; there is no elevated coronoid process in the 

 Edentata; the Dolphin and Porpois have not multicuspid teeth; 

 the Armadillo has not varied forms of teeth, nor has it double 

 fangs to its teeth, which also the fossil Megatherium has not. 

 Still, upon the whole, the above appears to be the general line of 

 distinction. Even if one or two of the above nine marks were 



