520 CRUSTACEA. 



We are unable to distinguish the separate localities of the P. spi?iosus 

 and P. pencillatus owing to the loss of labels through the opening of 

 the specimens at Washington, before the return of the Expedition. 



Family ASTACID.E. 



The Astacidae, in the form of the body and in general habit, 

 approach the Caridea. But the epistome is united to the shell 

 either side, although not so neatly as in the preceding families, since 

 this union is by a kind of adhesion of the parts, the edge of the shell 

 where it meets the epistome being distinct and somewhat projecting. 

 The basal scale of the outer antennas is, in general, much shorter and 

 narrower than in most of the Caridea. There is, however, a gra- 

 dation from the small size found in the Madagascar Astacoides, to the 

 expanded form in Paranephrops.^ The anterior legs are the largest, 

 and terminate in short hands. . The next two pairs have small 

 hands, but are scarcely stouter or longer than the remaining two pairs, 

 which are simply unguiculate; Unlike any of the Caridea, the 

 carapax in all the species has a strong transverse suture; and. in the 

 posterior dorsal region, traces of two longitudinal sutures may be gene- 

 rally distinguished, which are analogous to those in the Thalassinidea, 

 Paguridea, and iEglea. 



In the work of Edwards, this family includes only three genera, 

 Astacus, Nephrons, and Homarus. These genera are adopted by De 

 Haan, who at the same time points out other unnoticed distinctions 

 between them. In a recent elaborate revision of the Astaci by Erich- 

 son (Archiv. f. Nat., 1846, p. 86, and 375), other subdivisions are 

 proposed, as subgenera of the genus Astacus. These subgenera are 

 five in number. In three of them, the first segment of the male ab- 

 domen is without appendages, while they are present in the other 

 two. Of the latter, one subgenus (Astacus, mostly European), has a 

 pair of branchiae attached to the base of the fifth pair of legs; and another 

 (Cambarus, mostly American), is without this pair of branchiae. Of 

 the former, one genus (Astacoides, GuSrin), has the abdominal feet 



