OSTEN SACKEN ON WESTERN DiPTERA. 30 1 



Altogether different from that analogy, arising from the similarity of 

 meteoric conditions, are certain resemblances between the western fauna 

 (and especially that of California) and the fauna of Northern and Cen- 

 tral Europe, resemblances manifested in cases of generic and even spe- 

 cific identity. These cases derive their significance from the fact that 

 they are foreigu to the fauna of the Eastern United States; and they 

 are the more strange, as, far from being favored by any similitude of 

 meteoric and botanic conditions, they seem to exist in spite of differ- 

 ences in these conditions. Northern and Central Europe, in their cli- 

 mate and the character of their vegetation, are certainly more like the 

 northern Atlantic States of the Union than the western region. In such 

 cases, faunal resemblances are more than analogies, and seem to indicate 

 some relationship, some hidden genetic connection between the faunas 

 of Europe and the western portion of this continent. 



A European who has lived for some time in the Eastern States of the 

 Union, and crosses the Eocky Mountains for the first time, is soon struck 

 by the appearance of the Magpie, a European bird unknown in the 

 Eastern States. I am told that man}' parallel cases occur among birds. 

 Similar coincidences occur in all the orders of insects. 

 Plusia gamma is very common in California, and also occurs in Colo- 

 ! rado and Texas ; not in the Atlantic States. It is a well-known Euro- 

 pean species. The genus Parnassius occurs in the Coast Eange, the 

 | Sierra Nevada, and the Eocky Mountains ; it is found in the Alps in 

 1 Europe, in Sweden, and in Finland; it is not found east of the Mississippi. 

 I Argynnis, Melitcea, Lyccena, and the Satyridce, are by far more com- 

 I mon in California and in Europe than in the Eastern States. The Cali- 

 fornian Papilio zolicaon is almost the same as the European P. machaon. 

 , In Mr. Grote's Check List, etc. (p. 22), I find the statement that Ochria 

 I saucelitce Grote is a Noctna, with a horned clypeus, like the European 

 I Ochria flav ago Hiibner, and that no similar case is known to occur in the 

 Eastern States. 



Among the Neuropter.a, there is the European genus RhapMdia, quite 



common in California, and occurring in several species; it is unknown 



in the Atlantic States. Among the Orthoptera, the genus Locusta oc- 



j curs in Europe and in the Western Eegion, and not in the Atlantic 



States. Among the Diptera, I found in the Yosemite Valley a species 



of the genus Elliptera (Tipulidce), a genus discovered in Europe within 



the last fifteen years only, and not known to occur in the Atlantic 



States. A species of the European genus Silvius is common in Califor- 



| nia, and also occurs in Colorado; I have never seen a Silvius taken east 



of the Mississippi, although one is described by Wiedemann. The genus 



! Sphcerophoria (Melithreptus Loew, Syrphidce) is more abundantly repre- 



j sented in California and in Europe than in the Atlantic States. The 



I Calif ovmauLeptidce have a more European general appearance than those 



, of the Atlantic States. The above-mentioned Syrphus pyrastri is a 



1 common European insect, the larvoe of which live on Aphides; it is quite 



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