GENERAL KESUME. 85 



Rurales; and since this comprises, in the main, insects of exceedingly delicate 

 structure and of small size, their absence is by no means unaccountable. Yet, as 

 we shall see further on, there are intimations of the presence of some of their 

 caterpillars in amber, and an obscure and doubtful reference to a fossil Polyom- 

 matus from the beds of Aix. 



If we enquire where the allies of these nine fossil butterflies are now living 1 , 

 we must seek for those of four of them in the East Indies; for those of three of 

 them in America, and especially in that part lying on the confines of the tropical 

 and north temperate zones; for those of one of them in the north temperate zone 

 of both Europe-Asia and America; and for those of one in the Mediterranean dis- 

 trict; for those of two only, therefore, out of the nine, or less than one-fourth, in 

 the region where the fossils were discovered. Analyzing this point still further, 

 we notice that three out of the four species whose living allies are to be sought in 

 the East Indies come from the older deposits of Aix, and that only one of the two 

 remaining Aix species shows special affinities to American types; we thus find 

 here, as among other insects and among the plants, a growing likeness to American 

 types as we pass upward through the European tertiaries. 



The study of the floras of the European tertiaries has proceeded so far that in 

 most cases we are able to find, in the very beds where the butterflies occur, plants 

 which we may reasonably judge to have formed the food of these insects in their 

 earlier stages. In but a single instance is the family of plants, upon which it was 

 necessary, or almost necessary, to suppose the caterpillar fed, entirely absent from 

 tertiary strata; and since this family is the Cruciferae, which in its very nature 

 could scarcely have left a recognizable trace of its presence, the exception has no 

 force. 



After presenting these facts, for convenience sake, in a tabular form, we will 

 pass on to the enumeration of those fossils which have been referred to butterflies, 

 but whose exact position is still unsettled. 



MEMOIUS A. A. A. 8. 13 



