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 materials pos- 

 sessed 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, 

 whenever the place or person from whence they have been 

 received gives authenticity to the specimen, or adds anything 

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

 a collection. 



The various synonyma 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 original 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 



