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PROCEEDINGS OF THE NATIONAL MUSEUM 



Figure 21. — Ranges of Procambarus pecki and its allies: a, Gracilis Section; b and c, Mex- 

 icanus Section (b, Mexicanus Group; c, Cubensis Group); d, Procambarus alleni; e, Barb- 

 atus Section;/, primitive Cambarus (C. pristinus and C. obeyensis); g, Procambarus pecki; h, 

 troglobitic Orconectes. 



ical cephalic base of the mesial process, and initiated a subparallel 

 recurving of the latter and central projection. 



In the evolution of P. pecki (fig. 18), the shoulder was retained, 

 and the distal portion of the appendage became very slender; the 

 subapical setae, the cephalic process, and caudal elements were lost, 

 and the two remaining apical processes assumed positions similar to 

 those in P. alleni and the Mexicanus-Cubensis stock. 



