448 Stimpson on the Crustacea and Echinodermata 



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. Gambelii, 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 

 to Philadelphia for that purpose, to examine the typical 

 specimens of Randall's species, and those of De Saussure. 

 To Professor Dana I am indebted for much assistance, and 

 for the use of the few specimens of his types which were 

 particularly desired for comparison, — the admirable exact- 

 ness of his figures and descriptions rendering any further 

 means of identification in most cases unnecessary. 



Full descriptions will be here given of the new species 

 only, but notes are appended to several already known, 

 including remarks on characters which have been over- 

 looked by previous authors. Enough is given in most 

 instances to enable the reader to determine any known 

 California or Oregon species. 



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

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

 % Archiv fur Naturgesehichte, 1846, i. 99. 



J 



