1002.] AND ANCIENT GEOGRAPHY. 277 



ized one, and its distribution is more sharply limited than that of 

 Potamobius, it being found only in the eastern parts of North 

 America, Mexico and Cuba. 



Genus : Cambarus Er. 

 The genus Cambarus contains at present sixty-six well-known 

 species ; of a sixty-seventh, the group to which it belongs is doubt- 

 ful (C. clypeatus Hay, Missouri). The species form five groups 

 within the genus. 



Sixteen species belong to the first group, namely : 

 i. blandhigi (Harl.). 9. versutus Hag. 



2. hayi Fax. 10. spicu lifer (Lee). 



3. fallax Hag. 11. pellucidus (Tell.). 



4. clarki Gir. 12. acherontis Loennb. 



5. troglodytes (Lee). 13. wiegm ann i Er. 



6. lecontei Hag. 14. alleni Fax. 



7. angustatus (Lee). 15. evermanni Fax. 



8. pubescens Fax. 16. penicillatus (Lee). 



Eight species belong to the second group : 



1. cubensis Er. 5. gallinus Cock, and Port. 



2. carinatus Fax. 6. gracilis Bund. 



3. mexicamis Er. 7. carolinus Er. 



4. simulans Fax. 8. adve?ia (Lee). 

 To this group possibly belongs clypeatus Hay. 



Thirteen species belong to the third group : 



generic name of Astacus M. E., claim that Latreille (Consider, gener., etc., 

 1810; see Faxon, 1898, p. 662) has made this species, Astacics fluviatilis Fabr., 

 the type of the genus Astacus Fabr. This statement of Latreille, however, is 

 erroneous, since Astacus of Fabricius is a genus without lype, and remained such 

 until Saniouelle ( The Entomologists'' Useful Compendium, i8i9,p. 95) separated 

 Astacus and Potamobins (Lobster" and Crayfish). See Faxon, 1885 ; Ortmann, 

 «' Das System der Decapodon Krebse " (Zoo/. Jakrb. Syst., Vol. 9, 1896, 

 p. 430), and Stebbing (in Natural Science, Vol. 12, 1898, p. 239 ff.). 



