210 



ricum extricandam, stabilandamque, et affinitates naturales 

 eruendas ; auctore S. Drejer." 



It was referred to the publishing Committee. 



Dr. Gould also read extracts from a letter of Rev. Mr. 

 Mason, referring to specimens of Insects, some of which he 

 had forwarded to Dr. Gould. He mentioned others, which 

 he had not sent, from an impression that they were too 

 common. 



Professor Agassiz remarked on the mistake which naturalists 

 commit in overlooking the common productions of countries, in 

 Iheir search after rarities. It is the indigenous, and therefore 

 the most common, productions of countries, which are most wor- 

 thy of notice by native observers, and most likely to be interest- 

 ing to foreigners, and not those which are rarely met with. The 

 indigenous productions of America, for instance, are most the 

 objects of curiosity in Europe, and those of Europe in America. 

 The common household insects (Cimex, Blatta, &c.) are not with- 

 out interest when met with in distant countries, from the question 

 how far they have been changed by domestication and climate ; 

 which question can only be answered by the observation of many 

 specimens, and for the means of such comparison we might 

 search in vain in our collections. 



Count Pourtales exhibited a dissection of Natica heros, 

 showing the apparatus by which he supposed the animal 

 perforates shells. Dr. Jackson remarked, that he had dis- 

 covered slight signs of the existence of an acid in mollusca, 

 by which they might be aided in effecting the perforations 

 they make in shells and rocks ; he thought it possible such 

 an acid might be furnished by the fluids of their stomachs. 



Dr. Gould read descriptions of the following species of 

 Limniada?, from the Collection of the Exploring Expedition. 



Ancylus aduncus. Testa exigua, oblique conica, viridula, 

 striis radiantibus el striis concentricis decussata ; apice acuta, 

 valde incurvata : apertura ovato-rolundata. Long. -^, lat. ^jj, 

 alt. y\j- poll. Hub. Mountain streams, Madeira. 



Closely resembles A. Jluviatilis, and probably still more 

 A. radiatus, Guilding. 



