IV PREFACE. 



wise, its state is marked immediately after the letter by 

 which it is distinguished ; and if the sexes are known, it is 

 stated to be male or female. These particulars are followed 

 by the habitat, which is given as particularly as the mate- 

 rials possessed by the Museum permit. Those specimens 

 which have been presented to the Museum have the name 

 of the donor marked immediately after the habitat. When 

 there is no such indication, the specimens have been either 

 purchased or procured in exchange ; and in this case, when- 

 ever the place or person from whence they have been re- 

 ceived gives authenticity to the specimen, or adds anything 

 to their history, they are noted as being from such or such 

 a collection. 



The various synonyms have been given to the different 

 divisions of the class, and to the genera and subgenera and 

 species, and a reference made to the works in which they 

 have been characterized or described. 



In the adoption of the names for these divisions and for 

 the names of the genera and species, it has been thought 

 right to use, whenever it was possible, that which was first 

 used for the purpose. As far as regards the specific name, 

 there is comparatively little difficulty in the application of 

 this simple rule ; but ordinal, and especially generic names, 

 have been used by different authors in senses so widely dif- 

 ferent, and the groups which they are intended to designate 

 have been so variously extended and restricted, that it is no 

 easy matter to determine, where several names have been 

 used, which of them ought to be preferred. As every ori- 

 ginal observer will constantly make use of characters which 

 others may have overlooked, or not thought of so much 

 importance as further researches have shown to belong to 

 it, even when a generic name is used, it will of necessity be 

 often employed in a different sense, or with a more restricted 



