34 



According to Huxley the most important distinction is 

 presented by the podobranchiae, in which the stem (in 

 Astaais and Nephrops) is, as it were, completely split into 

 two parts longitudinally, one half corresponding with the 

 lamina of the crayfish [Poiamobms] gill, and the other with its 

 plume Ortmann expresses the same thing by saying that in 

 the Nephropsidae the podobranchiae are not coalesced with 

 the mastigobranchiae, and that in the Potamohiidae they are 

 coalesced. Moreover, in the former family the last thoracic 

 segment is firmly adherent to the rest, while in the latter 

 family it is movable. In Pota?nohtus the telson has a 

 transverse division which is wanting in yls^acus and Nephrops. 

 Between the two latter, on the other hand, there are well 

 marked distinctions. The branchial plume of the podo- 

 branchia of the second maxilliped is well developed in 

 Astacus, but very small or absent in Nephrops (Huxley, The 

 Crayfish, p. 281). The second antennae have a very small 

 exopod in Astacus, but a large one in Nephrops, and the 

 slender prismatic form of the front chelae which is character- 

 istic oi Nephrops is not shared by those oi Astacus. 



The species of Astacus sensu restricto at present known 



may be distinguished as follows : — 



/ Rostrum with teeth on the under surface, 



) I. A.americanus (Milne-Edwards). 



'■ i Rostrum without teeth on the under surface, 



/ Front chelae not pubescent on outer surface, 

 ) 2. A.ga^nmarus (Linn.). 



^' ' Front chelae pubescent on outer surface, 



3. A.capcnsiSy Herbst. 



( 



Astacus capensis, Herbst. 



1792. Cancer [Astacus) capensis, Herbst, Versuch einer 



Naturgeschichte der Krabben und Krebse, Bd. 2, 



Heft. 2, p. 49, t. 26, f. I. 

 1803. Astacus capensis, Latreille, Hist. Nat. Crust., v. 6, 



p. 240. 

 1837. Homarus capensis, Milne-Edwards, Hist. Nat. Crust., 



V. 2, p. 335. 

 1841. Homarus capensis, de Haan, Fauna Japonica, Crust,, 



p. 161. 

 1843. Homarus capensis, Krauss, Die Siidafrikanischen 



Crustaceen, p. 54. 

 1878. Homarus capensis (r), Huxley, Proc. Zool. Soc. London, 



for 1878, p. 754. 

 1895. Homarus capensis (r), Herrick, The American Lobster, 



p. 8. 



