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 ASTACI. 



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

 viz. : A. Ot'cgunus 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. Gatubetii Agassiz, first described as a 

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

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

 sonian Institution, Washington, D. C. A. nigrescens, A. Troicbridf/ii, and 

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

 lriiJ</ii in the Smithsonian Institution, the Museum of Comparative Zoology, 

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

 A. nigrescens and A. Klamathensis communicated by Stimpson. 



Distribution. The nearly related species A. leniusculus and A. Ti-owlridgii 

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

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

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

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

 regions of the Northwest, in Oregon, Washington Territory, and British 

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

 Astaci is A. GamMii, 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 physical 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 separating the waters of the Yellowstone from 

 those of the Snake River being very low, hardly above the level of the 

 ancient Yellowstone Lake.* 



Compared with the European species, the American Astaci have the 



* See W. II. llolmes's Report on tlie Geology of the Yellowstone National Park, in Twelfth Ann. Rep. 

 U. S. Geolog. and Geograpli. Survey of the Territories for 1878, Part II. p. 56, 1883. 



