350 MEMOIRS OF THE CARNEGIE MUSEUM 
These eight different forms are treated in the following pages, with the addition 
of one extralimital form, a variety of OC. propinqwus (C. propinquus sanborm). The 
recent and past observations made by the writer, together with those collated from 
other sources, are presented as completely as possible in the succeeding pages, thus 
giving a natural history of this group of animals, so far as found in the state of Penn- 
sylvania. It has always been the aim of the writer to support his conclusions by 
evidence secured within the state, but observations made outside of the state are 
sometimes introduced, where a gap was to be filled, or where they were of special 
interest. 
Ill. MorrHotoey AND CHOROLOGY OF THE PENNSYLVANIAN SPECIES. 
A. General Remarks. 
The crawfishes (as to the use of “crawfish” in preference to “crayfish” see infra, 
V1) of the state of Pennsylvania belong to the genus Cambarus* of Erichson (1846), 
of the family Potamobiide Huxley, including the freshwater crawfishes of the north- 
ern hemisphere. Faxon (1898) regards this as a subfamily, Astacinz, of the family 
Astacidx, which also includes the subfamily, Parastacinz of the southern hemisphere, 
now regarded as a family, Parastacide Huxley. There is some discussion as to the 
proper name of the family, depending on the use of the generic name Astacus Fab- 
ricius, or of Potamobius Samouelle, for the European crawfishes. The position of 
the writer was defined in 1902, (Proc. Amer. Philos. Soc. XLI, p.° 276, footnote). 
The question, however, has recently been finally settled by a discovery made by 
Miss M. J. Rathbun (Proc. Biol. Soc. Washington, XVII, 1904, p. 170), but not in the 
manner suggested by Miss Rathbun. The fact that the name Homarus was used 
first by Weber (Nomenclator Entomologicus, 1795), in place of Astacus Fabricius, 1775, 
makes Homarus a pure and simple synonym of Astacws, and according to the rule 
“once a synonym, always a synonym,” it remains a synonym. ‘There is no reason 
to make it “ desirable,’ as Miss Rathbun expresses it, to set aside the rule in this ease, 
The genus Cambarus, containing now about 70 species, has been variously sub- 
divided : by Girard (1852) into three groups; by Hagen (1870) likewise into three 
groups, which, howeyer, do not exactly correspond to those of Girard ; and by Faxon 
(18852) into five groups. Recently the present writer has divided the genus into 
six subgenera, namely: Paracambarus, Procambarus, Cambarus, Cambarellus, Faxo- 
mus, Bartonius. (See Proc. Am. Phil. Soc., XLIV, 1905, p. 91, et seq.; Ann. Carn. 
Mus. IT, 1905, p. 487; and Proc. Washington Acad. Science, VIII, p. 1, 1906.) 
* Erichson made this provisionally a subgenus, but expressed the opinion that it perhaps would better rank asa 
genus. Girard (1852) was the first to use Caumbarus as a generic name. 
