84 FOSSIL BUTTERFLIES. 



As a general rule the specimens thus far discovered are in a fair state of pres- 

 ervation, and especially are those parts preserved which enable us, with consider- 

 able confidence, to determine their exact affinities. Three of these insects belong 

 to the highest family of butterflies, Nymphalcs, four to the Papilionidge, and two 

 only to the Urbicolse. If it be considered probable that the lowest of these fami- 

 lies was the oldest, we can reasonably account for the scarcity of its members in 

 the tertiary strata by the fact that their almost universally robust and muscular 

 frame enables them to maintain flight when they have lost all but the merest stubs 

 of wings. They would thus seldom meet their end by falling into pools of water, 

 or if at last they did, it would be with fragments of wings whose affinities could not 

 be traced. This supposition would be strengthened on noticing that one of the two 

 fossil forms classed here, Thanatites vetula, belongs to a group of genera which 

 comprises the very feeblest flyers in the family; and by the further consideration 

 that two of the three fossil Nymphalids belong to the weak-winged Oreades. 

 Eugonia, as well as Pamphilites, were doubtless strong and bold flyers; while the 

 genera of Papilionidae were moderately endowed. To proceed further in the analy- 

 sis of their structural relations, two of the three Nymphales belong, as we have 

 said, to the highest group of butterflies, the Oreades, represented now by the dark 

 brown butterflies of our meadows; the remaining one to the Praefecti, a group 

 of gaily attired butterflies with angulated wings like our common thistle butter- 

 fly, the cosmopolite. Of the four Papilionidaa, three belong to the Danai; two 

 of these three to the group Fugacia, represented by our common yellow brimstone 

 butterflies; the third to the Voracia, or white butterflies of the garden, so destruc- 

 tive to cabbages and other cruciferous plants. The fourth Papilionid belongs to 

 the lower subfamily Papilionides ; not, however, to that group which contains our 

 swallow-tailed butterflies, but rather to an allied tribe, represented in America only 

 by the Parnasii of the Rocky Mountain region. The two Urbicolse are divided 

 between the Hesperides and Astyci, the former closely related to the dingy, sylvan 

 hesperians of early spring, seldom seen but by the naturalist; the latter to the 

 tawny, brisk little skippers busy around the flowers in June. 



But a single family of butterflies, then, is unknown in a fossil state, that of 



