OSTE-N SACKEN ON WESTERN DIPTERA. 3^)3 



the occurrence of Trimicra pilipes, apparently identicalwitb the European 

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

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

 common in all California in winter. 



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

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

 vsippi. 



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 Eocky 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 si^ecific 

 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 Limnoliic are not 

 distinguishable from eastern species. Trimicra pilipes, already men- 

 tioned, and Siimplecia punctipennis^ seem to be species of nearly 

 universal occurrence. Several Syrphidce, common in the Eastern 

 States, also occur in California. Asilidce and Tabanidce, 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 {Lep)tidce), and 

 the singular Epihates {BombylidcB), are worth noticing as being common 

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

 tinent. The remarkable genus Eachicerus {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 ^nd 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 Scellus {Bolichopo- 

 did(c) occurs alongside of the Californian Eulonclms [Cyrtidcv). With 

 the Californian DasylUs asiur {Asilidw) and Lapliria vultur (id.), I found 

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

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

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

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

 the same law, Basyllis flaricollis Say, which ranges from Canada to 

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

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



