271 



Westwood, J. 0. Kose-insects. Small 4to. Pamph. 



Westwood, J. 0, Synopsis of the Genera of British Insects. 8vo. London, 

 1839. 

 Wiedemann, C. R. G. Analecta Entomologica. 4to. Kiliai, 1824. 

 Wiedemann, C. R. G. Aussereuropaische Insekten. 8vo. 2 vols. 1828. 

 Wiedemann, C. R. G. Diptera exotica. Vol. 1. 8vo. Kilioe, 1821. 

 Wilson, James. Treatise on Insects. 4to. Edinburgh, 1835. 

 Wood, W. Index Entomologicus, 8vo. London, 1839. 



April 4, 1860. 



The President in the Chair. 



Prof. Agassiz alluded to the theory of Prof. Rogers on 

 subsidence and denudation as ingenious, and capable of 

 explaining the facts in the case, but did not see indica- 

 tions of these two phenomena, nor any proofs of such 

 extensive denudation as is required by it. 



He exhibited a series of fossils to show the distinctness of fau- 

 nae, explaining why it is not always correct to identify geological 

 periods by the identity of fossils ; two questions are involved in 

 the examination of this subject, one that of time or of period, the 

 other that of space or Umitation of faunae. 



Prehminary to the principal topic, he stated that he knew no 

 such thing as a variety in the animal kingdom, except such as 

 are stages of growth, within the Umits of species ; he instanced 

 as an example one of the meandrine corals (Mcmicma), and other 

 polymorphous types, which come within this law ; in 1200 echini 

 which he had examined and carefully studied, he had not found a 

 single variety which did not arise from an imperfect stage of 

 growth ; so in 6000 fishes, he had not seen a variety except in 

 coloration, which he had before shown was connected with their 

 growth. So that he would start with the propositions that ani- 

 mals do not vary, and that species remain within the limits of 



their type. 



He exhibited three species of Toxasfer, a spatangoid echino- 

 derm found in the lower cretaceous deposits, and which occurs in 



