of American Geologists and Naturalists. 99 



Prof. Ht 



Water Mollusca 



" Enumeration of the recent 



Europe, with observations on species and their distribution." 



Eight fresh- water species are enumerated as common to the two sides 

 of the Atlantic ; but as some naturalists doubt the identity of species 

 found under such circumstances, a portion of the paper is devoted to an 

 attempt to prove that the same species can occur in the most distant 

 localities, whether by transportation, former connexion of the regions, 

 distribution from more than one original centre, or by transmutation of 

 species. The two first are the most obvious, whilst the probabilities 

 against the third are stated to be not less than as ten thousand to one. 

 The Lamarkian hypothesis of transmutation is reviewed at some length, 

 and the fallacy of many of the arguments brought against it by Mr. Lyell 

 and others pointed out. 



For reasons given in the article, the Physadse alone are taken for 



the determination of the per centage of fresh-water shells common to 

 the two continents, and of these the proportion assigned is five per cent., 

 a proportion which is stated to obtain in the Brachelytra, a division of 



insects. 





^o opinion is offered for or against the theory of transmutation, this 

 being considered an open question, and one which has but a slight bear- 

 Mg upon geology ; because, were species transmutable, it would be 

 during the course of the geological periods, and that, whether organic 

 remains be assumed as at one time identical with recent species, but 

 n ow distinct, or as distinct at all times, the result and its applications to 

 geology must be the same. 



n umber of authorities are cited to prove that the same animals, in 



a number of instances, are found to inhabit distinct regions ; some phy- 



ogical points are discussed, and solutions offered to several imagin- 



bearin 



After a recess, the Hon. Natha 



W 



"us y on Waltershausen, dated Gottingen, December 18, 1843, 

 Ascribing his great work, called "jEtna and its Convulsions," 

 u pon which he has been occupied for seven years, and which 

 ^ * be published in the next six years, one portion each year. 



he work will be illustrated by a book of plates, containing fifty 

 °ur large engravings, (beautiful specimens of which were also 

 Presented,) to appear in six numbers; a topographical map in fif- 

 teen sheets, on a scale of 1 to 50,000, and a geological map in 



een sheets, with views, sections, and other drawings. 



