V.] INTRODUCTION. IxXXV 



Philippi's number of 500 as the standard of comparison 

 it is 41 per cent., after making some allowance on the 

 one hand for species unnoticed by Philippi but included 

 in my list, and on the other hand for species described 

 by him but not observed by me, although many of the 

 latter are unquestionably British. The discrepancy in 

 these results is the more remarkable when it is con- 

 sidered that only twelve years elapsed between the pub- 

 lication by Philippi and myself of our respective re- 

 searches. When the number and extent of similar in- 

 vestigations have been increased, and sufficient attention 

 has been paid to the discrimination of species, in order 

 to their identification with the names imposed upon 

 them by different authors, it is highly probable that a 

 still further correspondence will be found to exist between 

 the Testacea of the Mediterranean and British seas than 

 has been imperfectly indicated by me. One great diffi- 

 culty in making such a concordance has arisen from the 

 habit of merely collating the names given by authors, in- 

 stead of examining and comparing the specimens described 

 by them ; and I believe that many an unsuspected link 

 in the chain of specific identity would be detected by 

 pursuing the latter course of investigation. It was only 

 by mere accident, while I was lately looking over the 

 excellent collections of French sea-shells belonging to 

 M. Petit de la Saussaye at Paris and to Dr. Baudon 

 at Mouy, that I recognized, among some specimens 

 which they had received from M. Martin of Martigues, 

 and which he had procured by dredging in a deep part 

 of the Mediterranean off the coast of Provence, not only 

 the Buccinum Humphrey sianum of our northern sea 

 (under the name of B. Fusi/orme, Kiener), but also the 

 Rissoa abyssicola of Forbes, which had hitherto been 

 supposed to be exclusively confined to the Hebridean 



