ASTACUS. 135 



posteriorly, in A. IcniusntUts more cylindrical ; tlie carapace is k-ss 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. Icninsculus 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 \Qvy 

 nearly equal to half the distance from the cervical groove to the tijD of the 

 rostrum, while in A. Icnmsciilus the latter distance is twice and one half the 

 distance from the cervical groove to tlie posterior margin of the carapace ; 

 the areola is longer and narrower, considerably more than twice as long as 

 broad, while in A. kniusculns 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. 



Astaciia nitfrescens, Stisipson, Proo. Bost. Soo. Nat. Hist., VI. 87, February, 1857. — Joiirii. Bust. Soc. Nat. 



Hist.YI. 49-2, April, 1857. 

 Astaeua nigrescens, Hagen, 111. Cat. Miis. Comp. Zoo!., No. III. p. 'J3, PI. III. fig. 1G8, 1870. 

 AslacM nigrescens, Huxley, Tlie Crayfish, p. 244, fig. 61, C, F, I, fig. 62, C, F, 1880. 

 Astacus nigrescens, F.\xoN, Proc. Amcr. Aoad. Arts aud Sci., XX. 152, 1884. 



Known LoccdHies. — California: San Franciscoj Washington Territory : Fort 

 Steilacoom (Coll. U. S. Nat. Mus.). Alaska Territory: Oonalaska (Coll U. S. 

 Nat. Mus.). 



In most specimens the post-orbital ridges ai'e reduced to an anterior and 

 posterior spine, but in some there is a third sjaine between these two. The 

 ridge that represents the annulus ventralis of the female Cambarus is broadlj' 

 notched in the middle. 



A female specimen in the U. S. National Museum, from Fort Steilacoom, 

 Washington Territory (No. 2526), difibrs as follows from the typical form : 

 the sides of the rostrum are less inflated and more convei'gent, the acumen 

 shorter; the margin of the telson has only one synna 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. 



