ASTACUS. 131 



telson less clearly (Jiviclecl 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 branchiaj of A. Klumaihcnds, A. nif/rescem, and 

 A. Gamhcl'ii. In all of them the formula is the same as for A. fluviatiUs, 

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

 c/rescens the two anterior ones are short, but thick. Tliey are more highly 

 developed in A. Gamhclii 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 

 tlie 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 tlie rostrum not doiiticiilatcd. 



a. llostniin short, witli short acuincn. Post-orbital ridge witliout posterior spine. A. Kluiuaihensis. 



b. Rostrum long, with long acumen. Post-orbital ridge with a ])osterior sjiine or tubercle. 



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



hnig A. leniuseultis. 



0. Posterior spiue of post-orbital ridge small, sometimes reduced to a tubercle. Are- 

 ola one third as broad as long A. Trotcbridr/ii. 



B. Margins of the rostrum denticulated. 



a. Rostral acumen long. Posterior spine of post-orbital ridge ]n-omincnt. Chela not 



barbated ... A. nigrescens. 



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



1. Astacus Klamathensis. 



Plate VI. figs. 1, 2. 



Astacus Klamathomis, §timpson, Proc. Bost. Soc. Nat. Hist., VI. 87, February, 1S57- — Journ. Bost. Soc. 



Nat. Hist., VI. 491, April, 1857. 

 Antaeus Klamafheitsis, Spenck B.iTE, in Lord's "Naturalist in Vancouver Island and British Columbia," II. 



278, 18G6. (No description.) 

 ^Axtacus Klamutheims, Harem, III. Cat. Mus. Comp. Zool., No, III. p. !)3, PI. III. fig. 169, 1870. 

 Astaius Klamatheiish, F.\xoN, Proc. Amer. Acad. Arts and Sci., XX. 151, 1884. 



Known Locnli/ics. —Jdregon : KUmath Lake (Stimpson) ; Sikan Creek; 

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

 SjDokane 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 



