PLATE XXI. 

 Fenkstella Thyene. ' 



Page 50. . 

 Fig'. 1. A fragment of the iioii-coUuliferous face of a frond, natural size. 

 Pig'. 2. An enlarg-ement from the j)i"e<;eilinjj. 

 Fig. 8. An enlargement of the non-celluliferous face showing more slender branches. 



Lower Helderberg group. Sclwharie, iV. Y. 

 Fig. 4. An enlargement of the celluliferous face with an outline section of a branch at the left hand of the 



figm-e. 

 Fig. 6. A large funnel-shaped frond, natural size. 



Lower Helderberg group. Schoharie, iV. T. 



Fenestella Idalia. 



Page 52. 

 Fig. 6. The non-celluliferous face of a funnel-ahaped fi-ond, natural size. 

 Fig. 7. Aa enlargement of the non-celluliferous face. 



Lower Helderberg group. Clarksville, N. Y. 

 Fijf. ' 8. An enlargement of the non-celluliferous face showing slender striate branches. 

 Fig. 9. An enlargement of the non-celluliferous face of a frond, with stouter branches. 



Fenestlla Coronis. 



Page 61. 

 Fig. 10. A fragment of the non-celluliferous face of a frond, natural size. 

 Fig. 11. An enlargement of the non-celluliferous face showing the thickened base, and the entire surface free 



from striae. 

 Pig. 12. An enlargement from the non-celluliferous face. The upper part of the figure, from the outer ex- 

 tension of the frond, show.s elongate fenestrules and strongly striate granulose branches. 

 Pig. 13. An enlargement from the celluliferous face of the specimen tig. 11. 

 Ijower Helderberg group. Near ClarksvUle, iV". Y. 



Fenestella (Unitrypa) PKyEOuasoR. 



Page 5i. 

 Fig. 14. An enlargement_of the non-celluliferous face of a frond. 

 Pig. 15. An enlargement of the celluliferous face, showing the carinate branches, with the carinas expanded 



above and covei-ing the cell apertures, except in the upper part of the figure where they have 



been i-emoved. 

 Pig. 16. An enlargement of the celluliferous face, with the carina removed, exposing the cell apertures. 

 Pig. 17. An enlargement .showing the alate carinae, which in some parts are united by the extension of the 



marginal nodes into slender connecting bars. 

 Pig. 18. An enlargement from the ends of the branches showing the foi-m of the carinse with their lateral 



expansions. 



Lower Helderberg-gi-oup. Near Clarksville, N. Y. 



Fenestella quadrula. 



Page 53. 

 Fig. 19. A fragment of the n(in-(;ellulifei-ous face of a frond, natural size. 

 Fig. 20. An enlargement from the pi'eceding. 



Fig. 21. An enlargement of the celluliferous face with the carinas broken off, leaving the branches appar- 

 ently grooved. 

 Fig. 22. An enlargement of the celluliferous face, showing the presence of the alate carinae with the mar- 

 ginal crenulations. 



Lower Helderberg group. Near Clarksville, N. Y. 



