PLATE XVIII. 



Figs. 1-8. Representing a series of elongate turbinate or obconical forms, be- 

 ginning with the simple Cyathophycusreticulatus, Walcott — fig. 

 1, followed by the prismoidal Bictyophyton prismaticum, then 

 the similar form B. Conradi, sometimes with several nodes and 

 undulations in the upper part. Figs. 5, 6, 7 show a further de- 

 velopment of the number of nodes and annulations in the 

 species B. annulatum, B. nodosum and B. tuberosum. 



Fig. 2a. A transverse section of B. 'prismaticum, showing its regular octa- 

 gonal form. 



Fig. 4a. Shows the more compressed form of B. Conradi. 



Fig. 8. Represents the number and position of the vertical rows of tubercles 

 in B. tuberosum. All of the preceding forms are attenuate 

 below. 



Figs. 9-14. Represents three species having a spreading form, one of which 

 has been proved to possess a transverse diaphragm. 



Fig. 9. Bictyophyton Redfieldi has not yet been shown to possess the charac- 

 teristic diaphragm. 



Fig. 10. Thamnodictya Newberryi, preserving the general form of the cup and 

 a portion of the pedicel. 



Fig. 11. Ibid. The expanded portion of another specimen which is separated 

 from the basal portion. 



Fig. 12. Phragmodictya catilliformis, showing the form and ornamentation of 

 the cup, the summit of the basal portion and margin attach- 

 ment. 



Fig. 13. Ibid. Reduced, showing the base and superior portion separated at 

 the diaphragm. 



Fig. 14. Ibid. A specimen preserving the circular septum and a double ex- 

 tension of the walls, the lower one being less distinctly reticu- 

 late. (Reduced from the large figure given by Mr. Whitfield. 

 Bull. Am. Mus. Nat. Hist. p. 18, pi. 3, fig. 1, 1881.) 



Fig. 1. Cyathophycus reticularis, Walcott. Utica slate, N. Y. 



Figs. 2, 2a. Bictyophyton prismaticum, Hall. Chemung group, N. Y. and Pa. 



Figs. 3, 4, 4a. Bictyophyton Conradi, Hall. Chemung group, N. Y. 



Fig. 5. Bictyophyton annulatum, Hall. Chemung group, N. Y. 



Fig. 6. Bictyophyton nodosum, Hall. Chemung group, N. Y. 



Figs. 7, 8. Bictyophyton tuberosum, Conrad. Chemung group, N. Y. 



Fig. 9. Bictyophyton Redfieldi, Hall. Waverly group, Ohio. 



Figs. 10, 11. Thamnodictya Newberryi, Hall. Waverly group, Ohio. 



Figs. 12, 13 and 14. Phragmodictya catilliformis, Whitfield. Keokuk group, 

 Lower Carboniferous, Indiana. 



