BUTTERFLIES OF MONTANA. 123 



EXCHANGES. 



One of the best ways of adding to a collection is by the method 

 known as exchanging. A collector in one part of the country may find 

 species which are rare, or altogether unknown, in another part of the 

 country. By a system of exchanges with other collectors he is able to 

 supply the gaps which may exist in his collection. No one, however, 

 cares to effect exchanges with collectors who are earless or slovenly in 

 the preparation of their specimens, or inaccurate in naming them. A 

 collector who contemplates making an exchange should, as the first step, 

 prepare double lists, in one of which he gives the names and the number 

 of specimens of either sex of the butterflies which he is able to offer in 

 exchange; in the other he sets forth the things which he desires to 

 obtain. The first list is said to be a list of "offerta"; the second is a 

 list of "desiderata." As an illustration of the manner in which sudi 

 lists may be conveniently arranged, I give the following: 

 Offerta. 



Papilio turnus Male three; female four. Dimorphic var. glaucus, 

 male six. Colias alexandra, male four; female six. 

 Desiderata. 



Papilio nitra, female. 



Papilio brevicauda, orange-spotted var. 



The collector who receives these lists of offerta and disiderata will 

 be able to decide what his correspondent has which he desires, and what 

 there may be in his own collection which the correspondent wishes that 

 he can offer in exchange ; and the process of exchange is thus immediately 

 facilitated. 



Persons who exchange insects with others should always be ex- 

 tremely careful as to the manner of packing the specimens. Too much 

 care cannot be taken in preventing damage to specimens in transit. 



Holland, in "The Butterfly Book." 



