PLATE XVII. 

 MONTICULIPORA. 



(Page 577.) 



MOKTICULIPORA MAMMILLOSA, Hall. 



Fig. 1. Zoarium, natural size. 

 Fig. 2. A vertical section. x6. 

 Fig. 3. A transverse section. x6. 



These two sections show the generic characters. 



Hudson River group. Near Cincinnati^ Ohio. 



PRASOPORA. 



(Page 586). 

 Figs. 4, 6. A vertical and transverse section. x6. 

 Illustrating the characters of the genus. 



AMPLEXOPORA. 



(Page 577.) 

 Figs. 6, 7. A transverse and vertical section; illustrating the internal 

 structure of the genus. 



MONOTRYPELLA. 



(Page 581.) 

 Fig. 8. An enlargement of the surface. x6. 



Lower Helderberg group. N'ear Schoharie, N'. Y, 



PTYCHONEMA. 



(Page 583.) 

 Ptychonema tabulatum, Hall. 

 Fig. 9. An enlargement of .a portion, showing the peculiar corruga- 

 tions of the cell tubes. x6. 

 Lower Helderberg group. JVear Schoharie, JV, Y, 



652 



