756 THE BUTTERFLIES OF NEW ENGLAND. 



pointed out that the larvae of Libythea are not thickened on the thoracic 

 segments, have no thoracic tubercle and that the chrysalis terminates at 

 the anterior extremity in a single and not a double protuberance ; in other 

 words there is no apical notch. 



EXCURSUS XXIV.— FOSSIL BUTTERFLIES. 



And many an antenatal tomb, 

 Where l)utterflies dream of tlie life to come, 

 She left clinging round the smooth and dark 

 Edge of the odorous cedar bark. 



Shelley.— TAe Sensitive Plant. 



Fossil butterflies are the greatest of rarities. They occur only in 

 tertiary deposits, and out of the myriads of objects that have been 

 exhumed from these beds in Europe and America, less than a dozen and 

 a half specimens have been found. The great body of these deposits, as 

 is well known, are of marine origin, but at least thirty thousand specimens 

 of insects have been recovered from those beds which are not marine. 

 Over fifteen thousand insects from the one small ancient lake of Florissant, 

 high up in the Colorado Parks, have passed through my hands, yet I have 

 seen from there but seven butterflies. Each of these belongs to a genus 

 distinct from the others, as is also the case with all, or all but one, of the 

 butterflies found at lladoboj, at Aix and at Eott in the European tertiaries. 

 With two (European) exceptions, each represents an extinct genus, and 

 these two exceptions, Eugonia and Pontia, are genera found today both 

 in Europe and America. The species, however, are all extinct. 



One would hardly anticipate that creatures so delicate as butterflies 

 could be preserved in a recognizable state in deposits of hardened mud 

 and clay. Yet not only is this the case, but they are generally pre- 

 served in such fair condition that the course of the nervures and the color- 

 pattern of the wings can be determined, and even, in one case, the scales 

 may be studied. They are as a rule so well preserved that we may feel 

 nearly as confident concerning their aflfinities with those now living, as if 

 we had pinned specimens to examine ; and generally speaking the older 

 they are the better they are preserved ! 



There is, however, no great difference in their age. Aix and Florissant 

 are probably both oligocene and in any case can differ but slightly in age ; 

 one of the butterflies from Aix, Coliates, comes from beds a little lower 

 than the others and may be looked upon as probably the oldest butterfly 

 known. These two oligocene localities share between them a dozen but- 

 terflies, not to mention a caterpillar from Aix which has been considered 

 that of a butterfly. Eott, the next oldest (lower miocene) has furnished 

 only one butterfly ; and Radoboj (middle miocene) the remaining three. 



