EXPLANATION OF PLATE V. 



Paso, 



Oi;tiiis iif.supinata? -"•'' 



Kij;. 1. View of a dorsal valve, slif;btl.v exfoliated, but retaining the shell in great jiarl. 

 2. A cast of a dorsal valve, showing the muscular imprint. 



PnODUCTl'S ELEGANS -'"'^ 



Figs. 3-4. Profile and front views of a specimen referred to this species. 



nionUCTUS SEMIUETICUIATUS '-'''" 



Kigs. .VG. Vertical and cardinal views of a specimen referred to tliis species, showing the 

 form and surface character. 



Pl'.ODUC-rUS I..13VICOSTUS ? 



Figs. 7-8. Vertical and front views of specimens liaving the form and (diaracter of the sjxiic 



P[!<)I)UCTUS Fleminci var. Buhlingtonensis 



Fig. 9. View of a dorsal valve, showing the cardinal process. 



10. View of a ventral valve. 

 11-ia. Front and profile views of a similar individual, presenting the features of those fn 

 Burlington, Iowa. 



2C,r, 



Sl'I RTFERA sri'.IATA "■ • 



Fig. 13. Dorsal view of a spcciTuen somewhat crushed, hut showing the speeifu^ charactera 

 of the shell. 

 14. Ventral view of the same specimen. 

 1.^). Ventral valve of another individual, showing fewer bifurcations in the plications. 



Sl'IKirEHA sp. ? ~"^ 



Fig. Kl. View of th<! fragment referred to on page — . 



Si'irtll-EUA SETIGEHA 



Fig. 17. View of a small specimen somewhat compressed, hut preserving the surface char- 

 acters and somewhat the general form. 

 18. View of a larger dorsal valve, showing the form. 



AtIIYHIS SUnCJUADRATA ? 



Fig. 19. View of the dorsal side of a specimen referred to this species. 



20. Ventral valve of the same, showing the sinus as well as the general form of the shell. 



271 



