168 GEOGRAPHICAL ZOOLOGY. [part iv. 



There is also a considerable difference in the dependence to be 

 placed on the details given in the different classes of animals. 

 In Mammalia and Birds some degree of accuracy has, it is hoped, 

 been attained; the classification of these groups being much 

 advanced, and the materials for their study ample. In Keptiles 

 this is not the case, as there is no recently published work 

 dealing with the whole subject, or with either of the larger 

 orders. An immense number of new species and new genera of 

 snakes and lizards, have been described in the last twenty years ; 

 and Dr. Giinther — our greatest authority on reptiles in this 

 country — has kindly assisted me in incorporating such of these 

 as are most trustworthy, in a general system ; but until entire 

 Orders have been described or catalogued on a uniform plan, 

 nothing more than a general approximation to the truth can be 

 arrived at. Still, so many of the groups are well defined, and 

 have a clearly limited distribution, that some interesting and 

 valuable comparisons may be made. 



For Fishes, the valuable " Catalogue " of Dr. Giinther was 

 available, and it has rarely been attempted to go beyond it. A 

 large number of new species have since been described, in all 

 parts of the world ; but it is impossible to say how many of 

 these are really new, or what genera they actually belong to. 

 The part devoted to this Class is, therefore, practically a summary 

 of Dr. Gunther's Catalogue ; and it is believed that the dis- 

 coveries since made will not materially invalidate the conclusions 

 to be drawn from such a lai-ge number of species, which have 

 been critically examined and classified on a uniform system by 

 one of our most able naturalists. When a supplement to this 

 catalogue is issued, it will be easier to make the necessary altera- 

 tions in distribution, than if a mass of untrustworthy materials 

 had been mixed up with it. 



For Insects, excellent materials are furnished, in the Catalogue 

 of Mr. Kirby for Butterflies and in that of Drs. Gemminger and 

 Harold for Coleoptera. I have also made use of some recently 

 published memoirs on the Insects of Japan and St. Helena, and 

 a few other recent works ; and have, I believe, elaborated a more 

 extensive series of facts to illustrate the distribution of insects. 



