86 
include in their circuit the past as well as the present animal and 
vegetable population of the world. 
An example of this process has occupied a large portion of our 
attention during the past year. It appeared to be a proposition 
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 rightly 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 belong- 
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 phocz ; 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 Zhylacotherium Pre- 
vost. 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 ample 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 
