ART. XIII -WESTERN DIPTERA : DESCRIPTIONS OF NEW GEN- 

 ERA AND SPECIES OF DIPTERA FROM THE REGION WEST OF 

 THE MISSISSIPPI AND ESPECIALLY FROM CALIFORNIA. 



By C. R. Osten Sacken. 



PEEFACE. 



The Bipteraoi the Pacific coast are at present almost unknown. A 

 few species picked up during the visit of the Swedish frigate Eugenia, 

 probably in the environs of San Francisco, and described by Mr. Thom- 

 son ; some four dozen species, j)ublished by Mr. Loew in his " Centurise "; 

 a few other species, by Dr. Gerstaecker; and two lAmnobice, by me, con- 

 stitute about all we know of Californian DijHera. Even Chili is, in this 

 respect, much better explored, with the 556 species contained in Dr. 

 Philippi's publication. 



In the present publication, I give a survey of the collection of Diptera 

 which I formed during my recent western journey, and describe the 

 most remarkable forms. The majority of the species described belong to 

 California, where I collected the most ; the fauna of Colorado and of the 

 vast intermediate region will come in the second line only, the materials 

 being less abundant. However, the more I proceed with my study, the 

 more I am impressed with the fact that the western fauna is essentially 

 one, and that many of the characteristic forms of California sooner or 

 later will turn up in Colorado. 



The times and places of my collecting in California are as follows : 

 During the winter months (January to March, 1875), I collected a little in 

 Southern California ; my most active collecting, however, was confined 

 to the months of April and May, 1876, in Marin and Sonoma Counties; 

 a few days in Yosemite Yalley in June; and a couple of weeks in the 

 Sierra Nevada in July, especially about Webber Lake, Sierra County. 

 What I brought together is therefore but a small fragment of the fauna, 

 collected during a very limited season. And, yet, even this fragment 

 yields some very interesting facts concerning the geographical distribu- 

 tion of insects, discloses unexpected analogies and coincidences between 

 the fauna of California and those of Europe, Chili, and even Australia, 

 and unforeseen differences from the fauna of the Atlantic States. To 

 such facts, bearing upon the geographical distribution of insects, I pay 

 especial attention in the introductory paragraphs to each family; and, 

 at the end, I give a general survey of the results obtained. 



For the fauna of Colorado, I availed myself of very valuable mate- 

 rials kindly contributed by Mr. P. E. Uhler, Dr.A. S. Packard, and 



