South of Italy, and more particularly of Sicily. 208 
from our own epoch ? and how many species were destroyed by 
these catastrophes ? 3d, Do the species which are common to 
both periods present differences with reference to their relative 
abundance, or to their size and other characters, which, al- 
though in themselves considerable, are still not of sufficient 
importance to justify a specific separation ? 4th, What are 
the relations of the individual localities which afford fossils ? 
Are they all of the same age ? and can subdivisions be esta- 
plished in the tertiary formation of Southern Italy! dé, 
What are the relations of the tertiary formation of Southern 
Italy to other tertiary formations ? 
I am not in possession of sufficient data to answer the last 
question satisfactorily, but my investigations have led me to 
the following results respecting the four preceding queries. 
I. Comparative number of the Mollusca of the present epoch, 
and of the Tertiary Period. 
In the tertiary beds of Southern Italy, it is almost exclu- 
sively marine shells which are met with, and, of course, no 
remains of naked mollusca are found. If we subtract the lat- 
ter as well as the land and fresh water mollusca from the 
total number of living mollusca which have been observed, 
there remain— 
188 Marine Bivalves, 
10 Brachiopoda, 
11 Pteropoda, 
313 Conchiferous Marine Gasteropoda, 
15 Cirrhipeda, 
In all 537 Mollusca which could occur in a fossil state. 
The number of fossil mollusca hitherto found amounts to— 
231 Marine Bivalves, 
13 Brachiopoda, 
5 Pteropoda, 
322 Conchiferous Marine Gasteropoda, 
5 Cirrhipeda. 
576 
It thus appears that, at the time of the Tertiary period, the 
sea was but a little richer in mollusca than it is at present. 
