Pacific Shores of North America. 7 



of this family, all denizens of deep water, were until recently 

 known, one of which (the only one described in the " His- 

 toire Naturelle des Crustaces,") is found in the North Atlan- 

 tic, one in the Antarctic Ocean, and two in the seas of 

 Japan and Kamtschatka. Within the past ten years, how- 

 ever, no less than nine additional species have comcto light, 

 nearly all of which were found on the shores of California, 

 Oregon, and Russian America. Among these are some 

 gigantic and representative forms which tend greatly to 

 enlarge our views of the extent, importance, and relations of 

 the group. For our knowledge of these interesting Crusta- 

 ceans, we are chiefly indebted to Brandt of St. Petersburg. 



Among the fresh-water Crustacea we may notice the 

 fact, first observed by Dana * in Astacus leniusculus, that 

 the Cray-fish of the rivers running into the Pacific have 

 branchiae on the fifth pair of legs, and, like those of Europe, 

 are classed among the true Astaci. Agassiz f saw the same 

 thing in A. Ga?nbelii, and I have found it to be invariably 

 the case in the species of this region, among which there 

 are several not hitherto described in the Museum of the 

 Smithsonian Institution. Our eastern Cray-fish, on the 

 contrary, all belong to the genus Cambarus, having no 

 branchiae on the legs of the fifth pair, — a singular instance 

 of the coincidence of peculiarities of structure with those of 

 geographical distribution. Erichson J does indeed describe 

 two species of Cambarus from Southern Mexico, but we 

 have reason to suppose that these belong rather to the east- 

 ern slope of the Rocky Mountains. 



In the preparation of the following paper I have used 

 every means in my power to identify the species described 

 by previous authors, and have done this by actual compari- 

 son of specimens wherever it was possible. Through the 

 kindness of Dr. Bridges I was enabled, during a short visit 



* U. S. Exploring Expedition, Crust, i. 524. 

 t Proc. Acad. Nat. Sci., Philad. vi. 375. 

 % Archiv fiir Naturgeschichte, 1846, i. 99. 





