572 



NORTH AMERICAN INDEX FOSSILS. 



587. C. ashburneri Gabb. Cretacic. 



Subtrigonal. Average length 1.62 inches; height 1.25 inches. 

 Beaks subcentral. Anterior border slightly concave ; posterior 

 straight ; basal broadly rounded. Angle between the cardinal mar- 

 gins at umbo 90 . Regularly rounded concentric ribs numerous, 

 few, or absent. 



Very abundant in Chico of California and Washington. 



Fig. 785. a, Cymbophora utahensis, right valve ; b, <r, C. emmonsi, left valve. (After 



Stanton. ) 



588. C? utahensis Meek. (Fig. 785, a.) Cretacic. 

 Beaks incurved, with little obliquity. Growth lines fine and 



obscure. 



Coloradoan of Utah. 



589. C. alta Meek and Hayden. (Fig. 786.) Cretacic. 

 Thin-shelled. Dorsal slopes diverging from the beaks at an 



angle of about I io°. Extremities subangular or abruptly rounded. 

 Base forming a broad, semi-oval curve. Beaks very elevated, 



Fig. 786. Cymbophora alta y right valves, interior and exterior, X %• (After Meek, 



Surv. Terr., IX.) 



small or pointed, incurved, and very nearly central. Lunule and 

 escutcheon lance-oval, the latter the larger and bounded by a dis- 

 tinctly angular ridge. Surface concentrically striated. Average 

 length 2.6 inches; height 2.2 inches; convexity 1.2 inches. 

 Montanan : Colorado-Alberta. 



