434 Mr. R. M'Andrew on the Distribution of Mollusca. 



zoological provinces ; but this is no argument against the exist- 

 ence of such provinces : there have also been differences of 

 opinion as to the line of demarcation betvreen animal and vege- 

 table life. 



With regard to Mr. JeflPreya'a remark that he considers '^ the 

 marine fauna of Europe, Northern Asia, the Cis-Atlantic zone 

 of Africa and part of North America to have been closely related 

 at a comparatively recent epoch, and to form one common area 

 of origin/' I would beg to suggest that we have no proof of the 

 large area named ever having been simultaneously occupied by a 

 fauna more closely related together than the present ; and with- 

 out entering upon the question of the origin of species, I may 

 remark that most philosophers are agreed that these have origi- 

 nally been developed, or made their appearance, at a single point 

 or centre, and consequently that their tendency must have been 

 always at first to expand the limits of their range. The geo- 

 graphical range of the older species (those which have come 

 down to us from Tertiary times) is generally greater now in the 

 case of all the Southern (or Lusitanian) species, while the Arctic 

 species have suffered a diminution of their territory, at least in 

 latitude, since the " Glacial" age of geology. 



The assertion that M. Sars has discovered Cerithium vulgatum 

 and Monodonta limbata upon the coast of Finmark, if it is to be 

 understood that these species were living, must, unless they 

 were previously transported thither, be founded upon a mistake. 

 That they are actually indigenous in those seas is about as im- 

 possible as that the Myrtle, Gum Cistus, or Oleander should be 

 found growing naturally on the adjacent land *. 



In reply to Mr. Jeffreys's remark that, because the ocean at a 

 certain depth is of uniform temperature, it is only littoral and 

 shallow-water species that can be affected by climate, I would 

 observe that between shallow water, in its ordinary sense, and 

 those depths of the ocean where the temperature is invariable 

 and equal from the pole to the equator, a great interval exists, 

 and that in fact most, if not all the species of marine Mollusca 

 with which we are acquainted, are to be found living at depths 

 within the reach of climatal influence ; also that, notwithstand- 

 ing that the effects of climate become less in proportion to the 

 depth, yet, so far from finding tropical species in the abysses of 



* Cerithium vulgatum is a littoral and shallow-water species, though a 

 variety is occasionally to be met with as deep as 40 fathoms ; it inhabits 

 the coasts of the Atlantic, from Portugal to the Canary Islands, in addition . 

 to the Mediterranean, Monodonta limbata is a rare Mediterranean species, 

 which I have never had the good fortune to obtain myself, but have received 

 a specimen of from Sicily. The genus Monodonta is unknown in northern- 

 seas. 



