174 



MEDITERRANEAN PROVINCE. 



as the basis of his comparisons, and estimates the 

 Bivalves at 198, the Brachiopods at 5, the Gaste- 

 ropods at 191; in all 394 species. If we take the 

 more critical and newer enumeration of the "British 

 Mollusca," the same orders give 397. This close 

 agreement after an interval of so many years, and 

 after so much research, is somewhat remarkable, 

 and it is only on a careful examination of the 

 species composing these numbers that it is seen 

 what a great change our British list of Mollusks 

 underwent in the hands of Forbes and Hanley. 



If we add to Philippi from other sources and 

 enumerate the central Mediterranean Bivalves at 

 200 species, one-half will be also British, an amount 

 of agreement sufficient to indicate the Atlantic 

 character of the fauna, when it is remembered that 

 the comparison is made between the denizens of 

 zones separated by 5° of latitude. These two zones 

 extend respectively from 35° to 45° N. L., and from 

 49° to 59° N. L., making their extreme limits 

 14° apart. If, however, the British list is reduced 

 by some forty species, which are northern in their 

 British range, there remain only twenty-three spe- 

 cies to characterize our south-western assemblage, 

 or a rate of change of not more than from three to 

 four species for each degree of latitude, when com- 

 pared with the Mediterranean. Bivalves have a 

 broader and more uniform distribution than other 

 classes of their order. 



Comparing the enumeration given by Philippi 



