EXPLANATION OF PLATE 7 



All figures natural size, left valve. Figures 1 to 4 from locality 2975. 

 Figures showing gradation of Pecten wattsi Arnold and Pecten nutteri Arnold 

 into Pecten etchegoini Anderson. 



Fig. 1. Pecten etchegoini Anderson. From the type locality of the species, 

 Zapato Creek, Fresno County. 



Fig. la. Pecten etchegoini Anderson. 



Fig. lb. Pecten etchegoini Anderson, or P. etchegoini, var. wattsi Arnold. 

 Fig. lc. Pecten etchegoini wattsi Arnold. From the type locality of the 

 variety, Zapato Creek, Fresno County. 



Fig. 2. Pecten etchegoini wattsi Arnold. 



Fig. 8. Pecten etchegoini wattsi Arnold, or var. nutteri Arnold. 

 Fig. 4. Pecten etchegoini nutteri Arnold. From the locality from which 

 Arnold 's material was obtained, Zapato Creek, Fresno County. 

 Fig. 5. Pecten etchegoini nutteri Arnold. From locality 2982. 



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