ASTACUS. 135 
posteriorly, in A. /eniuseulus more cylindrical; the carapace is less punctate 
and less ciliate; the rostrum is shorter and broader, with shorter acumen, 
the distance between the lateral spines of the rostrum being equal to the 
length of the acumen, whereas in A. /emuseulus the length of the acumen 
much exceeds the distance between the lateral spines; the length of the 
part of the carapace posterior to the cervical suture is greater, being very 
nearly equal to half the distance from the cervical groove to the tip of the 
rostrum, while in A. deniwscu/us the latter distance is twice and one half the 
distance from the cervical groove to the posterior margin of the carapace ; 
the areola is longer and narrower, considerably more than twice as long as 
broad, while in A. /eniuseu/us it is much less than twice as long as broad ; 
the spines on the carapace behind the eyes are less developed, especially the 
posterior ones, and the chela is broader. 
4. Astacus nigrescens. 
Astacus nigrescens, Stutpson, Proe. Bost. Soc. Nat. Hist., VI. 87, February, 1857. — Journ. Bost. Soc. Nat. 
Hist:, VI. 492, April, 1857. 
Astacus nigrescens, HAGEN, Ill. Cat. Mus. Comp. Zool., No. II. p. 92, Pl. III. fig. 168, 1870. 
Astacus nigrescens, Huxuey, The Crayfish, p. 244, fig. 61, C, F, I, fig. 62, C, F, 1880. 
Astucus nigrescens, Faxon, Proc. Amer. Acad. Arts and Sei., XX. 152, 1884. 
Known Localities, —California: San Francisco. Washington Territory: Fort 
Steilacoom (Coll. U. 8. Nat. Mus.). Alaska Territory: Oonalaska (Coll. U.S. 
Nat. Mus.). 
In most specimens the post-orbital ridges are reduced to an anterior and 
posterior spine, but in some there is a third spine between these two. The 
ridge that represents the annulus ventralis of the female Cambarus is broadly 
notched in the middle. ‘ 
A female specimen in the U. 8. National Museum, from Fort Steilacoom, 
Washington Territory (No. 2526), differs as follows from the typical form: 
the sides of the rostrum are less inflated and more convergent, the acumen 
shorter; the margin of the telson has only one spine on each side; the hand 
is shorter, smoother, more coarsely punctate, the spines of the meros less 
developed; the branchial regions of the carapace and the abdominal pleura 
are more coarsely punctate. 
A male specimen in the same Museum is labelled “Oonalaska, W. H. 
Dall.” The rostrum of this specimen (No, 8954) is aborted and deformed, 
the chela longer than usual. The locality, if correct, is an interesting one. 
