130 A EEVISION OF THE ASTACID^. 



In the remaining species of Astacus the first abdominal appendages are 

 simply rolled, never bifid nor toothed at the end, neither are there hooks on 

 any of the thoracic legs in the male. 



THE NORTH AMERICAN xVSTACI. 



Six species of Astacns have been described from Western North America, 

 viz. : — A. Oreganus Randall, 1839 ; the type of this species was lost, and 

 the figure and description are insufficient for its determination ; it is perhaps 

 the same as A. leniusculus Dana. A. Gamhdli Agassiz, first described as a 

 Cambarus in 1852 by Girard; the types of Girard are in the Philadelphia 

 Academy. A. Icnimcuhis Dana, 1852 ; type in the collection of the Smith- 

 sonian Institution, Washington, D. C. A. niffrcscem, A. Troirhridr/ii, and 

 A. Klamuthensis, described by Stimpson in 1857 ; there are types of A. Trow- 

 hrhhjn in the Smithsonian Institution, the Musenin of Comparative Zoology, 

 and the Peabody Miiseum of Yale College ; Dr. Hagen examined types of 

 A. nigrescens and A. Klmvdliemk communicated by Stimpson. 



Distribution. — The nearly related species A. leniusculus and A. Troivbridgii 

 are found in the lower part of the Columbia River, Paget Sound, and adja- 

 cent regions. To the southward near the coast, in the neighborhood of San 

 Francisco, A. nigrescens appears to be the dominant species. It perhaps ex- 

 tends northward near the coast as far as Alaska. In the more elevated 

 reo-ions of the Northwest, in Oregon, Washington Territory, and British 

 Columbia, A. Klanudhfusis is found. The most eastern of the American 

 Astaci is A. Gambclii, which is found in the Great Salt Lake Valley and in 

 the upper waters of the Snake River, Idaho. From this region it has passed 

 over the divide into the Yellowstone Valley, and invaded the domain of the 

 Cambari as far as the confluence of the Yellowstone and Missouri Rivers. 

 An examination of the phj-sical geography of this region shows that the 

 migration of a Western species into the Mississippi basin at this point is no 

 difficult matter, the divide sepai'ating the waters of the Yellowstone from 

 those of the Snake River being ver}- low, hardly above the level of the 

 ancient Yellowstone Lake.* 



Compared with the European species, the American Astaci have the 



* See W. H. Holmes's Report on the Geology of the Yellowstone National Park, in Twelfth Ann. Rep. 

 U. S. Geolog. and Gengraph. Survey of tlie Territories for 1878, Part II. p. 56, 18S3. 



