PHYSAD^E. 15 



? POTAMOPHILA, Sw. "Shell resembling a Limnea, 

 but with a distinct fold on the pillar." Mr. Swainson gives 

 this name to certain species which he removes from Cono- 

 vulus to place among the Limneans. 



Lamarck has a hypothesis touching the origin of this 

 family,* which has induced some individuals to attack his 

 character, by which unphilosophic means his views were 

 to be subverted. These authors may have supposed such 

 ideas to be unworthy of a serious refutation, apparently 

 ignorant of the fact, that any views from so eminent a 

 source, are worthy of the profoundest consideration of less 

 gifted authors, who assume, rather than form their opi- 

 nions.f Every true naturalist must thank Mr. Lyell, the 

 distinguished British geologist, for the manner in which he 

 has discussed this question, his essay being that of a gen- 

 tleman, confined to the point at issue, unencumbered with 

 considerations which have no connection with it, and pre- 



of these sections, into those which breathe free air, and 

 those which oxygenate the system from water. I am of 

 the opinion that the same species can adopt either method, 

 according to the circumstances in which it may be placed. 



* Animaux sans vertebres, vol. viii. p. 378. 



f "If it is an obligation on science to proclaim the in- 

 tervention of a divine power in the development of the 

 whole of nature, and if it is to that power alone that we 

 must ascribe all things, it is not the less incumbent on 

 science to ascertain what is the influence which physical 

 forces, left to themselves, exercise in all natural pheno- 

 mena, and what is the part of direct action which we must 

 attribute to the Supreme Being, in the revolutions to which 



