516 Characteristics of the Central Zv6-Geographical, &c. [ August, 
Of the Orthopera there is a large number of species peculiar to 
the plains which I did not observe in the Pacific States; of these, 
Caloptenus spretus is thoroughly characteristic of the Central 
province. It does not occur in the Pacific and only breeds tem- 
porarily in the Eastern province, and its natural limits define 
well those of the province itself. It ranges up to lat. 53° N. on 
the North Saskatchewan and south to Southern Utah and Colo- 
rado. The exact limits of its distribution are given in the First 
Annual Report of the U. S. Entomological Commission. 
While we are still ignorant of the distribution of insect life 
between the hundredth meridian and the Pacific ocean, there 
seems good reason, from what we do know, and from the great dif- 
ferences in the flora, and the soil and climate, especially the rain- 
fall east and west of the Sierra Nevada, to regard this lofty range 
as the general point of separation defining two grand zodlogical 
provinces. Many groups 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 Arachnida 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 
plateau of North-eastern Asia. Among the insects there are a few 
Pacific forms which closely resemble European species, and which 
are not represented east of the Sierra Nevada. It should be borne 
in mind, however, that the Sierra Nevada does not present an 
absolute barrier, as a considerable number of species occur on 
each side of it, and it is well known that the Rocky 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 homogeneous, and the fauna of these Territo- 
_ ries 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 Cambarus, 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 Afodide is restricted to the Central prov- 
ince: none are found in the Mississippi valley, and none in Cali- 
