4o8 



PLATE IV. 



I, 2 and 3. Camarella owatonensis; showing ventral, dorsal and 

 lateral views. 



4, 5 and 6. Camarella bernensis ; ventral, dorsal and lateral views. 



7. Skenidium anthonensis x2 ; showing the cardinal area and delti- 

 dium, and ventral view of the same specimen. 



8, 9, 10. Crania halli ; (8) superimposed valves, lateral view, (9) in- 

 terior ventral and (10) interior of dorsal valve., 



II, 12. Productella minneapolis ; ventral valve and lateral view of 

 the same. 



13, 14. Discina concordensis ; dorsal valve (partly exfoliated) and 

 ventral valve. 



15, 16, 17, 18. Zygospira (?) aquila x2; dorsal, ventral and later?! 

 views, and (18) a section through the ventral valve of another specimen 

 near the median line. 



19 and 20. RhynChonella sancta ; anterior view and dorsal side show- 

 ing one heavy concentric line. 



21, 22 and 23. Rhynchonella minnesotensis ; (21) ventral view of an 

 average specimen; (22 and 23) dorsal and lateral of an antiquated indi- 

 vidual. 



24, 25. Leptsena minnesotensis ; interior of a dorsal valve, a longi- 

 tudinal section, and dorsal view of a large specimen. 



26, 27, 28. Leptaena prsecosis ; dorsal and ventral views and longi- 

 tudinal section of another specimen. 



29, 30, 31, 32. Leptaena recedens ; (29) ventral valve exterior, (30) 

 interior of same, (31) interior of a dorsal valve with the cardinal proces- 

 ses broken off, and (32) longitudinal section. 



33, 34, 3d- Leptaena saxea ; (ss) longitudinal section, (34) dorsal 

 view, and (35) interior of a dorsal valve. 



36, 37, 38. Strophomena halli ; exterior view from the concave side, 

 (S7) interior of a dorsal valve showing the triangular muscle scars, and 

 (38) a longitudinal section. 



39. Streptorhynchus subsulcatum ; dorsal view. 



