42 M. A. d'Orbigny on the Distribution of Littoral Mollusca, 



tagne. Some of the spores appeared to be uniseptate, but this 

 might arise from ocular deception. It grew in a loose soil in a 

 wood composed of hazel, beech and firs, in October last. 

 I am, Sir, your obedient servant, 



Wraxall, near Bristol, C. E. Broome. 



23rd December, 1844. 



VIII. — On the Laws which regulate the Geographical Distribution 

 of Littoral Mollusca. By M. Alcide d^Orbigny*. 



The author in the first place urges the importance of investiga- 

 tions on the geographical distribution of the coast mollusca, as 

 applied to general palaeontology. It is, in fact, in the laws which 

 at present regulate the geographical distribution of creatures that 

 we must logically seek by comparison for light upon the suc- 

 cessive animalization on the surface of the globe at all geological 

 periods, in order to substitute well-ascertained facts for doubtful 

 theories. 



The author selected, as the theatre of his observations. South 

 America, where he resided for eight years. Being at first of 

 opinion, a priori^ that the configuration of that continent, with 

 relation to its latitude, the abrupt or very gradual slopes of its 

 coasts, and the general currents which wash them, must have an 

 immense influence upon this question, he points out particularly 

 the characters which distinguish that part of the world, assisted, 

 for these currents, by M. Duperrey^s important map of the move- 

 ment of the waters, without which he would have been unable 

 to explain the anomaly of some facts. He presents in a table 

 the name and habitat of 362 species of littoral mollusca, which, 

 divided according as they belong to either of the two oceans, give 

 156 species peculiar to the Atlantic ocean, 205 species peculiar 

 to the Pacific, and a single species common to both seas. 



He examines separately the local faunas of the Atlantic and of 

 the Pacific. In the first he finds that the Falkland islands 

 have a peculiar fauna, that the fauna of the temperate regions 

 is more numerous than that of the hot regions, and that each of 

 these regions possesses from four to six times more peculiar than 

 common species. The Pacific presented identical results rela- 

 tively to the number of species peculiar and common to the hot 

 and temperate regions ; but the currents have there more influ- 

 ence on the partition of the species and on the separation of the 

 local faunas where their action ceases. 



His observations of the influence due to the orographic confi- 

 guration of the coasts upon the zoological composition of the re- 



* From the 'Comptes Rendus/ Nov. 18th, being an abstract by the author. 



