ASTAd's. I:; I 



U-lson less dearly divided by a transverse- suture, and (lie lir>t pair nl male 

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

 naceous tip. 



I have examined the branc-hia; of J. A7v;//^///(//.\/.v, A. itii/rrw/ix, and 

 A. Gambdu. In all of them the formula is the same as for A. y//"w////.v, 

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

 f/ri'xi'cns the two anterior ones are short, but thick. They are more highly 

 developed in A. Giuubclli 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. ./. 



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



a. Posterior spiue of post-orbital ridge loug and acute. Arcola cue half as broad as 



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

 ola one third as broad as loug ............ -/ 



B. Margins of the rostrum denticulated. 



a. Rostral aeumeu loug. Posterior spiue of post-orbital ridge prominent. Chela not 



barbated .... ............ A - 



b. Rostral acumen short. No posterior spine on post-orbital ridge. Chela barbated . 



1. Astacus Klamathensis. 



Plate VI. flg. 1, 3. 



Astacus Klamathensis, STIMPSON, Proc. Bost. Sue. Nat. Hist., VI. 87, February, 1S57- Journ. Bost. Soc. 



Nat. Hist., VI. 494, April, 1857. 

 Astacus Klu.mthe.isis, SPENCE BATE, in Lord's "Naturalist, in Vancouver Island and British Columbia," II. 



278,1866. (No description.) 



Axtaeu* Kl :l ,,i,<tl,,,*h, HA.GEN, III. Cat. Mns. Comp. Zool., No. III. p. 93, PL III. fig. 169, 1870. 

 s Kluiiiatlii'ii.ti*, FAXON, Proc. Amer. Aead. Arts and Sci., XX. 1 Jl, 1884. 



Known LocuJlllcs. 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 Hagen. It is common at Fort Walla 



