168 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 21, 



inhabitants of tlie earlier seas had a wider range north and south than 

 those of later periods, we must take into consideration the habits of 

 the animals of which we find the remains, and see whether the differ- 

 ences are due to greater powers of migration of the species of one 

 formation over those of others ; or whether they depend on the dif- 

 ferent depths below the surface at which the shells may be supposed 

 to have been originally deposited ; for we may expect to find most 

 widely diffused the remains both of animals capable of swimming out 

 to sea and of the inhabitants of deep water, which being less affected 

 by climate than those hying near the coast, can hye equally ui yery 

 different latitudes. 



The following table shows the number of the previously described 

 and of the new species of the four orders of ^lollusks, which include 

 most of the Portuguese secondary fossils, in each division of the geolo- 

 gical series ; and also the proportion per cent, which the previously 

 known species bear to the whole in each case. 



In the Hipjpurite limestone: — species. 



Gasteropoda 1 



Lamellibranchiata 9 



Brachiopoda — 



Cephalopoda — 



In the Subcretaceous series : — 



Gasteropoda 11 



Lamellibranchiata 23 



Brachiopoda 2 



Cephalopoda — 



In the Jurassic series : — 



Gasteropoda — 



Lamellibranchiata 6 



Brachiopoda 10 



Cephalopoda 24 4 



Total 86 61 



If we disregard the formations and look only to the character of 

 the animals, we shall find that of the Portuguese specimens collected, 



30 per cent, of the Gasteropoda, 



54 „ „ „ Lamelhbranchiata, 



86 „ „ „ Brachiopoda, 



86 „ „ „ Cephalopoda, 

 are kno-un to the north of the Pyrenees : thus it appears that the 

 STsimming Cephalopods and the i3rachiopods are diffused equally 

 widely, which can only be attributed to the latter living at great 

 depths. The Gasteropods prove to be the most local, which is 

 doubtless due to their 'mostly hving near the shore. The Lamelli- 

 branchs, which include species confined to the coast with others 

 livmg at greater depths, hold an intermediate place in the scale. It 

 is also to be remarked that the Brachiopods and Cephalopods are 

 found in company and almost by themselves in the Jurassic deposits ; 

 while in the cretaceous and subcretacous beds, in which Gasteropods 

 and Lamelhbranchs are abimdant, the two former orders are almost 

 entirely wanting. 



New 

 species. 

 4 .. 



Per centage of 

 knoNvn species. 



13 





41 















18 .. 





38 



... 18 .. 





56 







100 













2 .. 





75 



2 .. 





83 



4 .. 





86 



