PLATE IV. 



Favositks Helderberqi^.. 



Pago 8. 

 See Plates 5, 6. 

 Fig. 1. The lower side of a highly conical form which preserves the epitheca in. an unusual degree of 

 perfection. 



Lower Helderbevg group. ClarksxAlle, N. Y. 

 Fig. 2. The lower side of a more explanate form, from which the epitheca has been nearly removed by 

 weathering or solution, leaving the silicified cell walls and some of the septa. . Some of the 

 cells are entirely filled with siliceous matter and others are free. 

 Lower Helderberg group. Ctarkgnille, N. T. 



