290 DISTRIBUTION AND ATIOLOGY OF THE CRAYFISHES. 
or “stone crayfish,” und the latter by that of ‘ Edel- 
krebs,” or “ noble crayfish.” 
Milne Edwards, it will be observed, speaks of these 
two forms of crayfish as “varieties” of the species 
Astacus fluviatilis; but, even as far back as the year 
1803 some zoologists began to regard the “stone cray- 
fish” as a distinct species, to which Schrank applied the 
name of Astacus torrentiwm, while the ‘‘noble crayfish” 
remained in possession of the old denomination, Astacus 
fluviatilis ; and, subsequently, various forms of “ stone- 
crayfishes ’’ have been further distinguished as the species 
Astacus saxatilis, A. tristis, A. pallipes, A. fontinalis, 
&c. On the other hand, Dr. Gerstfeldt,* who has devoted 
especial attention to the question, denies that these 
are anything more than varieties of one species; but he 
holds this and Milne Edwards’s “‘ second variety ” to be 
specifically distinct from one another. 
We thus find ourselves in the presence of three views 
respecting the English and French crayfishes. 
1. They are all varieties of one species—A. fluviatilis. 
2. There are two species—A. fluviatilis, and A. tor- 
rentium, of which last there are several varieties. 
8. There are, at fewest, five or six distinct species. 
-Before adopting the one or the other of these 
views, it is necessary to form a definite conception of 
the meaning of the terms “‘ species ” and “‘ variety.” 
* “Ueber die Flusskrebse Europas.” Mém, de l’Acad. de St. Peters- 
burg, 1859, 
