OSTEIN" SACKEN ON WESTERN DIPTERA. 353 



the occurrence of Trimicra pilipes, apparently identical with the European 

 and probably with the North American T. anomala, although the latter 

 is comparatively rare in the Eastern States, while T. pilipes is exceedingly 

 common in all California in winter. 



In the whole western region, the genera Tabamis and Chrysops seem 

 to be far less abundant in species than in the region east of the Missis- 

 sippi. 



Of the anomalous family Blepharoceridce, all the species of which 

 seem to be rare and local, I have described a species from Yosemite 

 Valley and a new genus from the Rocky Mountains. 



After having detailed the peculiarities of the western, and especially 

 of the Californian, Dipterous fauna, it remains for us to examine what 

 they have in common with the eastern fauna. As a rule, cases of specific 

 identity between those regions occur more frequently in those same 

 families in which cases of specific identity are more frequent between 

 Europe and North America. Several Californian Limnobice are not 

 distinguishable from eastern species. Trimicra pilipes, already men- 

 tioned, and Symplecta punctipennis, seem to be species of nearly 

 universal occurrence. Several SyrpMdce, common in the Eastern 

 States, also occur in California. Asilidce and Tabaniclce, on the con- 

 trary, seem to be different in both regions, just as no species of these 

 two families is as yet known to be common to North America and 

 Europe. 



The genera Ceraturgus, Nicocles (Asilidce), Triptotricha (Lepticlce), and 

 the singular Epibates (Bombylidce), are worth noticing as being common 

 to both sides of North America, and not found yet outside of that con- 

 tinent. The remarkable genus Rachiceras (Xylophagidce) belonged in 

 the same category, until recently, when it was found in Spain. 



In the mountain-ranges which cross the western region from north 

 to south, some northern and subarctic genera and species are able to 

 reach very far south, and thus to come in contact with the forms of the 

 local fauna. In Yosemite Valley, at an altitude of 4,000 feet, the mixture 

 of truly Californian forms with those peculiar to the Sierra is only 

 beginning, the latter being comparatively rare. Around Webber Lake, 

 that is, farther north, and at an altitude of 7,000 to 8,000 feet, Californian 

 genera and species still occur in abundance, but more northern forms 

 are frequently met with them. The northern genus Scettus (Dolichopo- 

 didce) occurs alongside of the Californian JEulonclius (Cyrtidce). With 

 the Californian Dasyllis aslur (Asilidce) and Laphria vultur (id.), I found 

 Laphria rapax (id.), which looks like a northern form, although I may be 

 mistaken in my surmise. The specimens of Dasyllis astur, found at 

 that altitude, have much more yellow pile on their legs, neck, and pleurae 

 than those which were taken but little above sea-level. According to 

 the same law, Dasyllis flavicollis Say, which ranges from Canada to 

 Texas, has much more yellow on its legs and pleurae in the north than 

 in the south. Many interesting species were found round Webber Lake : 



