290 DISTRIBUTION AND jETIOLOGY OF THE CRAYFISHES. 



or " stone crayfish," and 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 torrentium, 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. Iristis, 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. 



3. 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." Mem. de l'Acad. de St. Peters- 

 burg, 1859. 



