

THE ANNULUS OF A MEXICAN CRAYFISH. 1 33 



tonins ; in C. clarkii, representing the subgenus Cambarus and in 

 C. montesiunce, representing the subgenus Cambarellus. It would 

 thus be premature to use the facts known as to the sperm recep- 

 tacle as a guide where they may clash with other criteria for 

 determining the history of the group. 



Observations upon the sperm pockets of the two other sub- 

 genera, Paracambarus and Procambarns, both ' well represented 

 in Mexico, are to be desired. 

 Baltimore, December 1, 1907. 



Explanation of Figures. 

 Figures are all drawn with camera lucida and the Zeiss lenses indicated : Fig. 1 

 with 2.90 mm. ; Figs. 2, 3, 4, 5, 6, 8 with 2A. ; Figs. 7, 9, 10 with 2D.; and 

 reduced to y$ diameter in Fig. 10 and ^ in the others. 



REFERENCES. 



1. Andrews, E. A. 



'97 Amer. Nat., 29, 1897. 



2. Ortmann, A. E. 



'06 Proc. Wash. Acad. Sci., VIII., 1906. 



3. '02 Proc. Amer. Phil. Soc, 41, 1902. 



4. '05 Proc. Amer. Phil. Soc, 44, 1905. 



5. Saussure. 



'57 Rev. et Mag. de Zool., 2d ser., IX., 1857. 



6. Martens. 



'72 Archiv f. naturgesch., XXXVIII., I., 130, 1872. 



7. Faxon. 



'85 Mem. Harvard Mus., 1885. 



8. '99 Proc. U. S. Nat. Mus., XX., 1899. 



9. Andrews, E. A. 



'06 Proc. Boston Soc. Nat. Hist., 32, 1906. 

 10. '06 Biol. Bull., 10, 1906. 



