INTRODUCTORY REMARKS. IX 



adoption of general conclusions ; the knowledge, however, that we 

 possess, scant as it is with regard to many vast districts, completely 

 bears out the rule that has been established in other groups of 

 insects, that while in tropical and in subtropical countries equally, 

 small and dull- coloured species are found, it is for the most part in 

 the tropics, properly so called, that (over and above these) large and 

 splendidly marked species are to be met with. The genus of this 

 group that of all others is distinguishable for brilliancy of clothing 

 and coloration is Octogonotes ; the species of this genus have been 

 discovered only in the tropical north of S. America. The same rule 

 applies (so far as we are able to fix the distinct regions of the species) 

 with regard to the genus Thrasygceus ; while, in Africa, the splendid 

 PJiysonychis smaragdina is found only in Senegambia and Old Cala- 

 bar (both within the tropics). 



To this general rule, however, the genera before us supply two 

 important exceptions : Loocoprosopus ceranriboides, the largest species 

 not only of the genus but of the whole group, has been found only 

 on the southern limits of the tropics, and the handsome genus Mo- 

 noplatus also is only to be met with in the same latitude, that of 

 Eio Janeiro ; these two examples (one of which is the example of a 

 single specific form) are distinct exceptions to what appears to ob- 

 tain as a very general law. With regard to the geographical range of 

 the species of the vast genus (Edionychis (the subject of the second 

 part), it may be urged that, in their case also, there is no infe- 

 riority of stature or coloration among the subtropical as contrasted 

 with the tropical species. This may perhaps for the most part hold 

 good; but in several instances at least, I believe that it may be 

 shown that this, however primd facie an apparent, is not a real 

 exception ; and that it will be seen, when that portion of the group 

 is specially considered, that some (and probably many) of the bril- 

 liant species composing it, which certainly abound in subtropical 

 latitudes, are merely local varieties of (if not almost identical with) 

 species that are met with in tropical districts, that is, that some 

 species at least of the genus have, in their several local modifications, 

 a range almost as extensive as the continent itself ; a fact that we 

 should, a priori, be led to expect from the abundance numerically of 

 individuals of these species. Thus, there is a certain parallelism of 



