Geological Society. 457 



universally true, that the oldest strata of the earth's surface con- 

 tained cold-blooded animals only ; and that creatures of the class 

 mammalia only began to exist on the surface after the chalk strata 

 had been deposited and elevated. And when, to a rule of this 

 tempting generality, a seeming exception was brought under our 

 notice, it became proper to examine, whether the anatomical line, 

 which enables us to separate hot-blooded from cold-blooded ani- 

 mals, had really been riglitly drawn ; and whether, by rectifying 

 the supposed characteristic distinction, the exception might not 

 be eliminated. The exception on which this very instructive point 

 was tried, consisted in a few jaw-bones of a fossil animal, which, 

 though occurring in the Stonesfield slate near Oxford, a bed belono-- 

 ing to the oolite formation, had been referred by Cuvier to the 

 genus Didelphys, and thus placed among marsupial mammals. 

 In August last M. de Blainville stated to the Academy of Sciences 

 of Paris his reasons for doubting the justice of the place thus as- 

 signed to the fossil animal. Founding his views principally upon 

 the number and nature of the teeth of the fossil, he asserted that 

 the animal, if a mammal, must come nearest the phocae ; but he ra- 

 ther inclined to believe it a saurian reptile ; following, as he con- 

 ceived, the analogies offered by a supposed fossil saurian described 

 by Dr. Harlan of Philadelphia, and termed by him Basilosaurus. 

 M. Valenciennes, on the other hand, asserted the propriety of the 

 place assigned by Cuvier to the fossil animal, although he made it a 

 new genus ; and gave to the species the name Thylacotherhitn Pre- 

 vostii. The controversy at Paris had its interest augmented when 

 Dr. Buckland in September carried thither the specimens in ques- 

 tion. From Paris the controversy was transferred hither in No- 

 vember, and principally occupied our attention at our meetings till 

 the middle of January. 



One advantage resulting from the araj^le discussion to which the 

 question has thus been subjected, has been, that even those of us 

 ■who were previously ignorant of the marks by which zoologists 

 recognise such distinctions as were in this case in question, 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 be deemed 

 presumptuous, if, without pretending to any power of deciding a 

 question of zoology, I venture to state the result of these discus- 

 sions. It appears, then, that some of the marks by which the under 

 jaws of Mammals are distinguished from those of Saurians are the 

 following : (1) a convex condyle ; (2) a broad and generally elevated 

 coronoid process, (3) rising near the condyle; (4) the jaw in one 

 piece ; (5) the teeth multicuspid, and (6) of varied forms, (7) with 

 double, fangs, (8) inserted in distinct sockets, but (9) loos(! and not 

 anchylosed with tliejaw. In all these respects the Suurians dittir ; ha- 

 ving, for instance, instead oi" a simple jaw, one composed of -iix bones 

 with [leculiar forms and relations, and marked by Cuvier MJtii di- 

 stinct names; having llie teeth Mith an expanded and simple I'ang, or 

 anchylosed in a gnjove, and so on. Of course, it will be sujjposed, 

 by any one acquainted with the usual character of natural groups, 



