Ixxxiv INTRODUCTION. [OH. 



between recent shells of Natica clausa from the North 

 Cape and fossil shells of the same species from Palermo. 

 It is an indisputable fact that whenever the Mollusca of 

 any part of the European sea-coast have been carefully 

 examined, the species which are there found exhibit a 

 greater conformity than had been previously supposed 

 with the species inhabiting more remote parts, the 

 general area being thus widened and every portion of it 

 brought into closer relation to the others. The former 

 test of percentage is in that case fallacious and no longer 

 to be depended upon. Thus we find that in Philippi's 

 invaluable work on the Sicilian Mollusca, which was 

 completed in 1844, 513 species of marine Testacea are 

 described. After making a small deduction for dupli- 

 cates (e. g. six out of eight species of Anomia, and some 

 JRissoce), about 500 species may be regarded as distinct. 

 The treatise appended to the last volume of that work 

 contains a table of comparison between the Mollusca of 

 the Mediterranean and those of the British seas ; and 

 in this table 127 out of the above number of 500 are set 

 down as belonging to our fauna. This gives a rate of 

 only about 25 per cent. The result of my own exami- 

 nation of the marine Testacea of another part of the 

 Mediterranean* is very different from that of Philippi 

 especially when it is taken into account that my exami- 

 nation only occupied three or four weeks, while Philippi 

 was engaged for many years in a continuous investiga- 

 tion. The total number of species which I found or ex- 

 amined on the Piedmontese coast in 1855 was 375 ; and 

 of this number I identified no less than 205 as British. 

 This gives a rate of nearly 55 per cent. ; and taking 



* "On the Marine Testacea of the Piedmontese Coast, "Ann. &Mag. 

 N. H. , February 1856, p. 155-188. An Italian translation by Professor 

 Capellini has been published at Genoa. 



