158 REPORT — 1856. 



its principal development at their point of meeting, and this I believe to be 

 neither more nor less than what actually occurs. The point at M'hich the north 

 temperate or boreal, and the south temperate faunas meet, I conceive to be 

 about lat. 50°, or at the British Channel, which marks the limit of some of 

 the most characteristic northern forms, viz. Buccinum undatum, Fusus 

 antiquus, Cyprina Islandica, &c., as well as of the genera Haliotis, La- 

 chests, Cah/ptrcea, Venerupis, Gastrochccna, Auricula, and numerous species 

 of southern type. Supposing my view to be correct, it is at once seen why 

 there can be no peculiar species in the Celtic (or as I would rather call it), 

 the English or intermediate fauna. It is difficult to lay down an exact line 

 of division between one animal province and another, the transition being 

 gradual; but I would consider the "intermediate" fauna to be contained 

 between the 45th and 55th parallels of latitude, which will include the larger 

 portion of the Bay of Biscay and a considerable part of the North Sea. All 

 species which attain their maximum of development within these limits I 

 would consider legitimately to belong to it, and among the most characteristic 

 of these may be mentioned Purpura lapillus, Natica nionilifera and iV. nitida, 

 Trochus zizyphinus. Lacuna piiteolus, L. pallidula, all the British Pholades, 

 Mactra solida, Tellina ctassa, Pecten opercularis, P. pusio, and Venus stri- 

 atula. 



Although, as already stated, the transition from one fauna to another takes 

 place gradually, the change is much greater at certain geographical points 

 than at others, and the neighbourhood of Cape St. Vincent is remarkable as 

 the northern limit on the Atlantic coast of about a hundred southern species, 

 including the following genera : — 



Solemya. Siphonaria. Ranella. Conus and 



Cardita. Sigaretus. Mitra. Cyprsea (except the 



Chama. Crepidula. Columbella. sub-genus Trivia). 



Spondylus. CancoUaria. Pollia. 



Though Cardita and Mitra reappear in the Polar seas represented each by 

 a single species, and Cancellaria under the form Admete. Cymha extends 

 to the neighbourhood of the rock of Lisbon ; Hingicula to Vigo ; Triton, 

 Turbo, Cassis, and Lithodomus to Asturias ; Adeorbis, Haliotis, CalyptrcBa, 

 Lachesis, Gastrochcena, Venerupis, Galeomma, aui.i Avicula to the south 

 coast of England. 



The circumstance of so many characteristic forms disappearing at Cape St. 

 Vincent, may perhaps be accounted for by the change which there takes place 

 in the direction of the coast and consequent set of the current. It will be 

 noticed that the disappearance of species is all in one direction, and that the 

 point in question is not known to form the southern limit of a single species; 

 also that nearly all the genera enumerated as not passing it are to be found 

 six or seven degrees further north in the Mediterranean. 



A circumstance analogous to what occurs at Cape St. Vincent takes place 

 about the South of Scotland with reference to northern forms of Mollusca. 

 Of 135 Norwegian species which extend to Scotland, no less than 42 are 

 absent from the South of England ; and this fact is, I conceive, to be explained 

 by the change in the nature of the sea-bottom, which may also account for 

 the circumstance that many species, and among them the peculiarly northern 

 forms of Trichotropis, Cemoria, and Pilidium, are common to the coast of 

 Norway and the Hebrides, and even extend as far south as the Clyde, 

 while they are altogether absent from, or but very rarely found upon the east 

 coast of Scotland. 



The Mediterranean fauna may be considered a branch of the north tem- 

 perate Atlantic, agreeing with it in its general character, though possessing 

 some peculiarities, a natural result of its isolated condition. 



