OBSEBTED AT MOGADOE. 171 



to investigate whether the set of tides or currents may or may not 

 have contributed to this result. 



Next to this strong aifinity of the Mogadorian Molluscous 

 Fauna with that of the British shores, succeeds its relation (2ndly) 

 to that of the Canarian, (3rdly) to that of the Madeiran, and 

 (4thly) to that of Senegal. Having, for example, according to 

 the following very incomplete list, 26 species in common with 

 Britain alone, Mogador has about as many more in common with 

 Britain and the Canaries, the Madeiras and Senegal, in various 

 combinations. Again, it has 6 or 7 in common with the Canaries 

 alone, and from 33 to 37 more jointly with the same islands, with 

 the Madeiras, Senegal, and Britain, &c. &c. (see for the rest the 

 subjoined Table) ; offering thus on the whole, in 90 species, 53 in 

 common with the British seas, 39 to 44 with the Canarian, 27 with 

 the Madeii'an, and 17 with the coast of Senegal. 



This latter number would at once be larger but for the difficulty 

 attending the exact identification of several of Adanson's Senegal 

 species. And doubtless further researches on the spot would add 

 to his list several Mogadorian shells, which, considering the pre- 

 sence of others on the shores of Senegal, have been very probably 

 overlooked or neglected by him. In the meantime it is most 

 interesting to find already, from the materials in hand, two or three 

 common English and Mogadorian shells, Scrohicularia piperata 

 (G-m.), Tapes Pullastra (Mont.), and perhaps also Mactra stul- 

 torum, L. (of which last, however, a single valve has been also 

 found by Mr. M'^ Andrew in Teneriffe), reaching down even to 

 Senegal, 15° below Mogador, and far within the tropics. 



The authorities consulted for habitats in the following list are, 

 1st, Forbes and Hanley's ' British Mollusca ' (referred to as F. H.) 

 for British shells; 2ndly, D'Orbigny's very imperfect article 

 "Mollusques" in Webb and Berthelot's ' Histoire,' &c. vol. ii. 

 part 2 (referred to as "W. B.), with Mr. M«^ Andrew's far more 

 exact and copious list of marine Testaceous Mollusca collected 

 during a month passed in the Canary Islands in 1852, in his 

 ' Essay on the Geographical Distribution of the Testaceous Mol- 

 lusca in the Nortli Atlantic and neighbouring Seas ' (Liverpool, 

 1854, Bvo), reprinted as an appendix to the British Museum's 

 * List of the Shells of the Canaries,' London, 1854 (quoted as 

 M'^Andr.) ; 3rdly, Adanson's ' Histoire ' for the shells of Senegal 

 (quoted as Adans.) ; and 4thly, for Madeira entirely, and for the 

 Canaries partly, my own observations and collections. 



12* 



