1916] 



Packard: Mesozoic and Cenozoic Mactrinae 



269 



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Figs, la to If/. Graphs showing ratios of lengths to heights: la, Spisula 

 catilliformis ; 16, Mulinia densata ; lc, Martra californica; Id, Spisula ash- 

 burnerii; le, Schizotliaerus nuttallii; 1/, Spisula selbyensis ; Ig, variations 

 in the position of the beaks in S. selbyensis. 



