242 MM. Pictet and Humbert on the Fossil Fishes 
1. The fauna of Hakel has greatest resemblance to that of 
Comen in Istria. Nevertheless it presents a greater proportion 
of living genera, and may thus be contluded to be the more 
recent of the two. 
2. The fauna of Sahel Alma is unquestionably related to that 
of the Chalk of Westphalia. 
3. Both one and the other differ to a greater extent from that 
of the Chalk of England. 
4, These differences and resemblances may be partly owing 
to geographical causes, and partly to the respective ages of the 
formations. The former would tend to augment the relations 
with Comen, and to diminish those with the Chalks of more 
northern countries, and would consequently weaken considerably 
the importance to be attached to the resemblances. 
In spite of doubts so engendered, the precise limit to which 
it would be impossible to lay down, our general conclusion is 
that the faunas of the Lebanon are, both the one and the other, 
intermediate between those of Istria and those of the Upper 
Chalk, and that, consequently, their position is most probably in 
the Middle Cretaceous formation. 
And here we have to deal with a question both difficult and 
embarrassing. What is the relative age of our two Lebanon 
faunas? And which is the more ancient ? 
Had the labours of Botta resolved this question, and were we 
already possessed of sufficient stratigraphical proofs, we should 
not now be forced to have recourse to the hazard of a palzonto- 
logical analysis, which is the more embarassing since it leads us 
to a result quite opposed to that which the above-named author 
somewhat prematurely regarded as probable. M. Botta be- 
lieved the fauna of Sahel Alma to be the more ancient. The 
comparisons which we have lately made, and which have brought 
us to the conclusion that the fauna of Comen is more nearly re- 
lated to that of Hakel, while that of Sahel Alma more especially 
recalls the fauna of the White Chalk, lead us on the contrary to 
consider the first the more ancient. It is to be hoped that a 
complete geological survey of these countries will put an end to 
this uncertainty. 
General Paleontological Considerations. 
The study of organic development throughout the course of 
geological time shows that the different classes of the animal 
kingdom are far from presenting a history uniform in this re- 
spect. The epoch, in particular, during which the modifications 
which have more powerfully affected the organism have taken 
place would seem to have been by no means the same for the 
