A.STAC1 s. i:;i 



telson less clearly divided by a transverse suture, and the first pair of male 

 appendages are more closely rolled, with a more pointed and membra- 

 naceous tip. 



I have examined the branchiae of A. Klamathensis, A. nigrescens, and 

 A. Gambelii. In all of them the formula is the same as for A. fluviatilis, 

 there being three rudimentary gills on each side of the thorax. In A. ni- 

 grescens the two anterior ones are short, but thick. They are more highly 

 developed in A. Gambelii than in any other species of Astacus examined, 

 presenting an interesting approach in structure to the perfectly developed 

 gilL Each of the rudimentary gills is much larger than in any other species, 

 and is jointed at a short distance from the base. At the joint there are, in 

 the intermediate pair, two short lateral branches, one on each side; in the 

 anterior and posterior pairs the main stem bears one lateral filament. 



I find no trace of appendages on the first abdominal somite of the 

 female in any of the American species of Astacus. 



The five American species of Astacus may be distinguished as follows : — 



A. Margins of the rostrum not denticulated. 



a. Rostrum short, with short acumen. Post-orbital ridge without posterior spine. A. Klamath nsis 

 6. Rostrum long, with long acumen. Post-orbital ridge with a posterior spine or tubercle. 

 a. Posterior spine of post-orbital ridge long and acute. Areola, one half as broad as 



long 1 leniusculus, 



/3. Posterior spine of post-orbital ridge small, sometimes reduced to a tubercle. Are- 

 ola one third as broad as long A. Trowbridgii . 



B. Margins of the rostrum denticulated. 



a. Rostral acumen long. Posterior spiue of post-orbital ridge prominent. Chela not 



barbated A. nigrescent. 



b. Rostral acumeu short. No posterior spine ou post-orbital ridge. Chela barbated . A. Gambelii, 



1. Astacus Klamathensis. 



Plate VI. ties. I, 2. 



Astacus Klamathensis, Stimpson, Proc. B ist. S ic Nat. Hist., VI. 87, February, 1857- — Journ. Bost. Soc. 



Nat. Hisl . \ I 194, April, 1357. 

 Astacus Klamathensis, Spence Bate, in Lord's "Naturalist in Vancouver Island and British Columbia," II. 



278, L866. (No description.) 

 Astacus Klamathensis, Bagen, 111. Cat. Mus. Comp. Z ml., No III. p. 93, PI. Ill fig. L69, 1870. 

 Astacus Klamathensis, Faxon, Proc A.mer. Acad. Arts and Sci., XX. lJl, 1884. 



Known Localities. — Oregon: Klamath Lake (Stimpson); Sikan Creek; 

 Des Chutes River. Washington Terr.: Fort Walla Walla; Wenas Valley; 

 Spokane Falls. British Columbia: streams east of the Cascades (Bate). 



Stimpson's types were found in Klamath Lake by Dr. Newberry. One 

 of these, a female, was described by Ilagen. It is common at Fort Walla 



