INTRODUCTION. 3 



A. S. Packard. 5. Tvpos of nine .species of Mr. Giraixl and Professor W. 

 Stimpson, kindly communicated to mc by Professor W. Stimpson. 



The Astacidaj in the collection of the Smithsonian Institution I have 

 not yet seen. 



I have described thirty-eight species, — thirty-two Cambari and six 

 Astaci. Eleven species, all Cambari, are new. There are six species 

 — four Cambari and two Astaci — which I have not seen. 



Among the twenty-eight species of Cambarus which I have examined 

 I have seen the two forms of the male, and the female of twenty-three 

 species, the first form of the male and the female of one species. There 

 are two species, of which I have seen only the first form of the male ; 

 of one species I have seen only the second form ; of five species I have 

 seen but single specimens ; of all others, a considerable number. 



Among the four species of Astacus which I have examined I have 

 seen of one species both the male and female ; of another species, the 

 male only ; of the other two species, the female only ; and in all cases 

 only a few specimens of each species. 



This monograph, as I am convinced, is very far from embracing the 

 entire number of species living in North America. May new explora- 

 tions soon render my work incomplete. 



