58 M. Alcide J'Orbigny on Living and Fossil Molluscs. 



ever enjoyed better opportunities of studying these animals 

 in every point of view, than M. d'Orbigny. His early years 

 were spent on the shores of the ocean, while a journey of 

 seven years' duration in South America, and immense collec- 

 tions, have furnished him with numerous points of comparison. 



" The geographical distribution of molluscs is of great im- 

 portance, because, proceeding from the known to the un- 

 known, it is calculated to make known to palaeontology, by 

 the laws which regulate the geographical distribution of liv- 

 ing beings, what has taken at the different epochs of animals 

 appearing on the globe. I shall here mention, in a general 

 way, some of the principal results with whicli my numerous 

 investigations on this subject have ali*eady furnished me. 



" The study of terrestrial animals has proved to me that 

 the species, restricted by limits more or less extensive, were 

 distributed each accoi'ding to special* zones of tempei-ature, 

 complicated, nevertheless, by influences determined by the 

 orographic form of continents and their phytographic com- 

 position. In general, the number of species decreases in 

 proportion as we recede from the warm regions and approach 

 the cold regions. t 



" The study of marine pelagic animals, or such as belong 

 to deep seas, has in like manner demonstrated to me that of 

 the cephalopods.J notwithstanding the number of species 

 which pass indifferently from one ocean to another, more 

 than two- thirds of each sea are peculiar to it. These num- 

 bers evidently prove, that the limits of fixed habitation still 

 exist in respect to animals, which their power of locomotion, 

 and pelagic habits, would distribute throughout every sea, if 

 Cape Horn on the one hand, and the Cape of Good Hope on 

 the other, were not, in their southern position, altogether be- 

 yond the torrid zone, which nearly all the species inhabit, 

 and thus form a bai'rier which they are unable to pass. We 

 have, therefore, the certainty that uniformity of temperature, 



* See my observations on this subject, Mollusques de mon Voyage dans I'Ame- 

 rique Meridionale, p. 215. 



t Same work. 



\ iFemoir read to the Academy of Sciences, 19th July 1841, and inserted in 

 the Monographic des Cephalopodes Acetabulijeres. Introduction. 



