PACKARD.] GEOGEAPHICAL DISTRIBUTION OF PHYLLOPODA. 367 



to Southern Utah and Colorado. The exact limits of its distribution 

 are given in the First Annual Eeport of the United States Entomologi- 

 cal Commission. 



While we are still quite ignorant of the distribution of insect life be- 

 tween the hundredth meridian and the Pacific Ocean, there seems good 

 reason, from what little we do know, and from the great differences in 

 the Hora, and the soil and climate, es[)ecially the rainfall east and west 

 of the Sierra Nevada, to regard this lofty range as the general point of 

 separation deiining two grand zoological provinces. Many groui)s of 

 insects abounding west of the mountains do not occur east, except in 

 isolated cases. Of a number of Myriopods found on the Pacific coast 

 none occur east, and so of the Arachuida so far as known, and Dr. 

 Thorell, who has worked up some of the spiders of Colorado, was struck 

 by the general similarity of some forms to those occurring in the 

 l^iateau of jSTortheastern Asia. Among the insects there are a few 

 Pacific forms which closely resemble European species, and which are 

 not represented east of the Sieri-a IS'evada. It should be borne in 

 mind, however, that the Sierra Nevada does not present an absolate 

 barrier, as a considerable number of species occur on each side of it, 

 and it is well known that the Eocky Mountains are but a slight barrier 

 to the distribution of the animals on either side, the fauna of Colorado, 

 Northern Utah, Wyoming, Montana, and Idaho being quite homogene- 

 ous, and the fauna of these Territories the same on each side of the 

 high mountain ranges traversing them. 



Among the fresh-water Crustacea the Astaci of the Pacific slope, as 

 is well known, belong to the European genus Astacus, those east of the 

 Sierra Nevada to the genus Camharus, which is so richly developed in 

 the eastern provinces, especially in the Mississippi Valley. 



The distribution of the fresh-water Phyllopoda is of peculiar interest. 

 The family Apodidce is restricted to the Central province; none are 

 found in the Mississippi Valley, and none in California. Of the four 

 species of Apus all inhabit the Central province; Ap7is caqualis lives on 

 the j)lains of the Eocky Mountains, and also at Matamoras, in Mexico. 

 It is a curious fact that Apus lucasaiius Pack, not only occurs at Cape 

 Saint Lucas, Lower California, but is also an abundant species at Ellis, 

 Kansas. This is a parallel case to the presence of certain birds at Cape 

 Saint Lucas which, as observed by Professor Baird, belong to the Central 

 rather tha.n to the Pacific province. Of the genus Lepidurus there are 

 two forms {L. eouesii and L. Mlobatus) characterizing the plains. JJ. 

 couesii occurs in Northern Montana and in Utah, and is allied to the re- 

 cently described Lepidurus maorourus from Archangel, Eussia, accord- 

 ing to Lilljeborg. 



The eastern limits of the Central province extend to near the 97th 

 meridian in Kansas and Nebraska, according to the writer's observations. 



The following species inhabit this province : 



Limnetis mucronata. Lepidurus hilohatus. 



hrevifrons. Apus newherryi. 



gracilicornis. cequalis. 



Ustlieria compleximanus lucasanus. 



mexicana. longicaudatus. 



helfragei. Brancliinecta color adensis. 



morsei. Undahli. 



JEulimnadia texana. Streptocephalus texanus. 



Lepidurus couesii. Thamnocephalus platyurus. 



