204 Dr A. Philippi on the Recent and Fossil Mollusea of the 
It must be granted that future investigations will probably 
add a larger number to the list of fossils than to that of liv- 
ing species ; but, on the other hand, it is to be remembered 
that the tertiary period lasted a much longer time, and that, 
during its continuance, species became extinct and new ones 
were added. It is therefore extremely probable that, dur- 
ing the tertiary period, the sea was neither poorer nor richer 
in mollusca than it is at present.* 
The relative numbers belonging to the principal orders 
were somewhat different from what they are at present ; thus 
we have— 
During the ter- At the pre- 
tiary period. sent epoch. 
Marine Bivalves, . ; 3 z ; 0.40 0.35 
Brachiopoda, z Z ; : : 0.024 0.02 
Pteropoda, . : : : 0.01 0.02 
Conchiferous Marine Gasteropoda, ; 0.56 0.58 
Cirrhipeda, . d : : é F 0.01 0.03 
The Bivalves and Brachiopoda, therefore, predominated 
more at a former period than they do at present, and the 
Gasteropoda and Cirrhipeda are now more numerous than 
they were formerly. Hence, I think, we may conclude that, 
at the time of the Tertiary period, there were fewer coasts in 
existence, and that the submarine land, which is now con- 
verted into dry land, then consisted chiefly of shallows. 
II. Relative numbers of the extinct and living species. 
Of the 537 marine mollusca which could occur in the fossil 
state, I have not met with the following 169 (not quite a 
third part) among the Tertiary petrifactions of Southern 
Italy :— 
BIVALVES. 
Clavagella balanorum, Scac. Teredo Bruguieri, D. Ch. 
angulata, Ph, palmulata, D. Ch. 
Teredo navalis, Z. Pholas candida, LZ. 
* If we were to adopt this principle as the basis of our calculations, 
and to divide the whole geological series only into the tertiary, chalk, 
Jura, old secondary, and transition formations, the number of fossil spe- 
cies would amount to at least five times as many as that of the living ; 
and if, on a moderate calculation, we were to reckon the latter at 8000, 
the former would amount to about 40,000 species ! 
