G. GENERAL NATURAL HISTORY AND ZOOLOGY. 331 



next to number one. The third group comprises a few arctic 

 and circumpolar species of cosmopolitan genera. The fourth 

 group embraces species common to both the Pacific and At- 

 lantic States. 



A careful inquiry into the facts has led Dr. Packard to the 

 conclusion that, among the Lepidoptera at least, there is the 

 same close relationship between the fauna of California and 

 Europe as has been noted in other groups of animals, as well 

 as of plants ; Eastern America, on the other hand, being more 

 closely related to Eastern Asia than it is to Western America. 

 Similar facts have been observed in regard to the Neuroptera 

 and the Crustacea Limulus being found only on the east- 

 ern side of Asia and America ; and, while the European ^s- 

 taus belongs to California, Cambarus occurs only east of the 

 Rocky Mountains. 



The fishes of Eastern Asia and Eastern America show a 

 closer relationship than those of the two sides of the Amer- 

 ican continent, a& do the batrachians and reptiles of North- 

 eastern Asia and Northeastern America. It is, however, 

 in the plants that these relationships can be most distinctly 

 indicated ; and the theory suggested by Professor Gray, and 

 adopted by Dr. Packard, is to the efiect that co-specific or co- 

 generic forms in California, Europe, and Asia are the rem- 

 nants of a southward migration from j^olar tertiary lands, 

 during tertiary, and even, perhaps, cretaceous times ; and, in 

 proportion to the high antiquity of the migrations, there 

 have been changes and extinctions causing the present anom- 

 alies in the distribution of organized beings which are now 

 so difficult to account for on any other hypothesis. For this 

 reason. Dr. Packard thinks it not improbable that those spe- 

 cies of insects which are more or less cosmopolitan are the 

 most ancient ;' and that the anomalies in the distribution of 

 Limulus accord with its isolation from other Crustacea ; geo- 

 logical extinction having gone hand in hand with geograph- 

 ical isolation. The Limulus was a common form in Europe 

 in the Jurassic period; and in the next lower (the Permian), 

 we find other forms of the same group and some Trilobites. 

 Dr. Packard expects much light to be thrown upon this sub- 

 ject by the careful study of the tertiary deposits of the West, 

 and of the arctic tertiary and cretaceous formations. 5 X>, 

 August, 1873,453. 



