20 DfesCRIi'TIO.V OF 



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Fig. 1. PRODUCTUS WORTHENI. 635 



.1 



1 a. Profile view of a specimen. 



1 b. Ventral valve of the same. 



Fig. 2. PRODUCTUS MESIALIS. 030 



2 a. The interior of .a dorsal valve, from which the ventral, valve has been 



exfoliated. 



2 b. Profile view of the ventral valve. 



2 c. Ventral valve of a large individual, which is somewhat broader than 

 the prevailing forms. 



Fig. 3. PRODUCTUS SETIGERUS. 038 



3. Dorsal side of specimen, showing the beak and nmbo of the opposite 

 valve. 



Fig. 4. PRODUCTUS SEMIRETICULATUS. 037 



. 



4 a. Interior of dorsal valve, from which most of the shell has been exfo- 

 liated, leaving an impression of the external markings. 



. 

 Fig. 4. PRODUCTUS SETIGERUS? var. KEOKUK. 039 



4 b. Cardinal view of a ventral valve. 



4 c. Another view of the same specimen, looking upon the centre of the 



valve. g ' 8 



Fig. 5. ORTHIS KEOKUK. 040 



.,' .-oi'J 



5 a. View of a ventral valve, which is broken transversely across a little 



below the beak. 



5 b. Ventral valve of a specimen which is partially concealed at the mar- 

 gins. 



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