PREFACE v 



tions of a larger island, or where communication between the islands 

 may be, or at an earlier period, has been, possible. Under such condi- 

 tions subspecific forms may be found; but on the mainland where 

 there is no evidence of a gradation from one form to another, sub- 

 species may not be accepted. 



The Author has dwelt upon this point, because it may occasion 

 surprise to some who examine these volumes, to find how few sub- 

 species comparatively have been accepted, and it seemed best to explain 

 how these are regarded, and what, as the Author conceives it, is the 

 only method by which they can be produced. In the present work there 

 are altogether fifty-five complete monographs, with about six hundred 

 species, for it was deemed best that every genus should be treated 

 monographically. Of course these vary greatly in importance and in 

 the number of their species, from one only, to over eighty, but the 

 average would be about twelve to a genus. Each member of the Order 

 has been treated after the following method. First a general review is 

 held of the genus accepted, the type fixed and description given ; then 

 remarks are made on the appearance and general habits of the species 

 the genus contains, followed by a review of the literature and the 

 geographical distribution, and a key by means of which it is possible 

 that all the species of that particular genus may be recognized. Then 

 each species is taken up in regular sequence, its synonymy given and 

 the type locality and geographical distribution recorded ; the present 

 location of the type if existing, is then told, after which the peculiar 

 characters of the species if it possesses any, are given, followed by 

 such remarks as may be necessary, upon the relationship the species 

 under review may have with some other in the genus ; then a full 

 description and measurements of the type if possible, concluding with 

 an account of the habits so far as they may be unquestionably known. 



Of course it is not to be expected that a work such as this can be 

 produced solely by the unaided efforts of one individual no matter 

 how long or conscientiously he may labor, and many times he is obliged 

 to rely upon the aid of his colleagues as the work progresses. Con- 

 sequently during the past five years the Author has been assisted in 

 many ways by a large number of his scientific friends. And here he 

 may be permitted to express the great pleasure and gratification he 

 felt at the universal courtesy and kindness he received at all the great 

 Museums in Europe and the East, as well as in those of his own land, 

 by the officers who had charge of the great collections. Every possible 

 facility was given him and unrestricted access to the collections at all 

 times ; and wherever the Author went, his simple request proved to be 



