vf, INTKOUIJCTION. 



catalogue of those noticed by authors as existing in other 

 portions of North .America. 



Several American and European Zoologists have, however, 

 at diflerent times, given the results of their investigations in 

 various scientific journals, thus making it important for us 

 to examine nmnberless papers, pubhshed in different cities 

 of Europe and America. We have, in all cases, sought to 

 discover and give due credit to every one who has in tliis 

 manner made known a new species^ but as possibly some 

 author may have published discoveries in a journal we have 

 not seen, we must at once announce our conviction, that 

 the task of procming and reading all the zoological papers 

 scattered tlu-ough the pages of hundreds of periodicals, in 

 many different languages, is beyond our power, and that no 

 one can reasonably complain when we take the liberty of 

 pronouncing for ourselves on new or doubtful species without 

 hesitation fif-om the sources of knowledge to which we have 

 access, and from om- own judgment. 



From the observations we have already made, we are in- 

 duced to beUeve that a considerable number of .species are yet 

 undescribed while others, now imperfectly known, require a 

 closer investigation and a more scientific arrangement, and it 

 will be a part of our task to give an accoimt of the former 

 and defiaie the position of the latter. 



The geographical range which we have selected for our in- 

 vestigations is very extensive, comprising the British and 

 Russian possessions to the north, the whole of the United 

 States and their territories, California, and that part of MexicQ' 

 north of the tropic of Cancer, we having arrived at the con- 

 clusion that in undertaking the natm-al history of a country, our 



