40 INTRODUCTION. 



in the branch of knowledge to Avhich he had devoted 

 hunself, which has forever associated his name with the 

 history of Zoology in the United States, and which ought 

 to entitle him to the honor of bemg styled its fomider. 

 His pubHshed works, commencing about the year 1817, 

 continue through a period of eighteen years untU liis 

 death in 1834 ; and embrace descriptions of a vast num- 

 ber of animals until then entirely imknown, or but 

 imperfectly miderstood. The invertebrated classes 

 received the greater part of liis attention, and his con- 

 tributions to their history must, necessarily, form an 

 important portion of the means of any writer who shall 

 seek more fully to elucidate them. The major part of 

 the subjects described in this volume were first described 

 by him ; and so fully had he occupied the groimd, that 

 the additions to our knowledge of species made during 

 the twelve years, since his decease, have not exceeded 

 the number contributed by him, although within that 

 time many new mquirers have commenced their investi- 

 gations, and large districts of country, which he never 

 examined, have been explored. His descriptions are for 

 the most part so accurate, and his observations so just, 

 that there is httle left to his successor except to brmg 

 them together in their proper order. Some obscuiity, 

 indeed, attends several of his species, in consequence of 

 his not having uniformly placed specimens in a pubhc 

 depository for reference ; for, when objects resemble each 

 other so closely as do several species of the genera Helix 

 and Pupa, it is very difficult to distinguish them T)y 



