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University of California Publications in Geology [Vol. 12 



GEOLOGIC RANGE 



In the discussion of the geologic range of the Pacific Coast echi- 

 noids it is found that the subject may be treated under two topics: 

 first, the range of the genera, and, second, the range of each species 

 in detail. The first is of major importance in the west coast province, 

 especially during the Tertiary period, for it is only within certain 

 definite time intervals that these genera occur. This is graphically 

 shown by figure 1. In treating the second topic it is not necessary to 

 discuss each species separately, and their stratigraphic position can 

 be expressed better in tabulated form. 



Cidaris 



Strongylocentrotus 



Scutella 



Astrodapsis 



Dendraster 



Heraiaster 



Scliizaster 



















































J 



















































Fig. 1. Geologic ranges of the more important genera of Pacific Coast 

 echinoids. 



Explanation. — Horizontal extension of curve represents geologic time. The 

 curve with the highest vertical extension indicates the genus with greatest 

 number of species and probably the dominant genus at that time. The broken 

 line indicates incompleteness in the fossil record, and the probable range of the 

 genus. 



