attention to the exploring of the bottom of the sea, commencing with 

 our own coasts, and occasionally extending my excursions to those of 

 neighbouiing countries. In laying before the Society some of the 

 results of my investigations, I may be allowed to mention, as an evi- 

 dence that they have not been altogether fruitless, the fact, that the 

 marine fauna of the Canary Islands had been represented to be of 

 African type, but is proved by me to be much more closely allied to that 

 of the MediteiTauean ; and, in consequence, the line, marking on a 

 physical map the limit of the tropical fauna, has had to be altered from 

 the north to the south of those islands. 



There exists a considerable analogy between the distribution of 

 animals (particularly those which, in consequence of a lower organiza- 

 tion, enjoy but very limited power of locomotion,) and of plants. The 

 fauna, as well as flora, of the arctic and antarctic regions being poor in 

 genera and species, but rich in the number of individuals, while the 

 tropics furnish the greatest variety of form in both departments. Also, 

 similar conditions in distant parts of the world present representative, 

 but not identical, species and genera, both in the animal and vegetable 

 kingdoms ; and, although the region of Australasia would appear at 

 first sight to form an exception to this rule, a closer observation will 

 shew that its real peculiarity consists in its representing a more 

 ancient state of things, such as may probably have existed in other 

 parts of the world at some period prior to the creation of man. 



This view is, I believe, borne out by the general character of tlie 

 plants and vertebrate animals, whilst among the moUusca may be 

 quoted the characteristic genus Trigonia, not met with elsewhere in a 

 living state, but largely represented in the oolites of this country. 



It is well known with respect to land vegetation, that a difference of 

 elevation compensates for difference of latitude, and that arctic forms 

 are repeated in the same or similar species on the lofty mountains of 

 the temperate and even of the torrid zones. It might be supposed that 

 the analogy would hold good with respect to the marine mollusca, but 

 such is the case only to a very small extent. The temperature of the 

 ocean, at great depths, being uniform in all latitudes at about 40 de- 

 grees of Fahrenheit,* it is very evident, that although the inhabitant of 

 shallow seas in temperate regions may, by descending to a greater 

 depth, procure a similar average temperature either in higher or lower 

 latitudes, the same resource would not bo available to the natives of- 



• Cuptain Uoiiham stales, that at 200 fathoms it averages 50" and 53°, no matter what 

 the surlttce temperature may bo; ami below that ilepth, diininishes till it reaehos the miui- 

 niiiin of 10" at UOO to 1000 fatlioins. 



