430 



NORTH AMERICAN INDEX FOSSILS. 



Differs from Byssonychia in the absence of the anterior byssal 

 opening and lateral teeth. 



The Ambonychiidae differ from the Aviculidae in being equi- 

 valved and without anterior wing. Ordovicic. 



183. A. bellistriata Hall. (Fig. 561, a, b.) Ordovicic. 



Beaks very prominent and strongly incurved. Surface marked 

 only by radiating striae. 



Middle Trenton : New York. Middle Galena of Minnesota 

 and Cincinnati Group of Indiana. 



FlG. 561. a, b, Ambonychta bellistriata, left valve and anterior view; c, d, A. amyg- 

 dalina. (Minn. Surv.) 



184. A. amygdalina Hall. (Fig. 561, c, d.) Ordovicic. 



Differs from A. bellistriata in its larger size, less incurved beaks, 

 and less angular post-cardinal margin. 



Trenton : New York, Canada. Middle Galena of Minnesota. 



LV. Anomalodonta Miller. 

 Closely similar to Ambonychiam outline and general appearance 

 but differing in possessing a byssal opening. Distinguished from 

 both Ambonychia and Bysso?iychia in the absence of both cardinal 

 and lateral teeth. Ordovicic. 



