PLATE VI. 



Page. 



All the flgurers on this plate except No. 18 are xi8. 



Figs. 1 to 6, 12 and 13. Ehenidictta mutabilis Ulr". '125 



1. Tangential section of an old and thick example of the usual form of this species. Figs. ' 



6 and 12 represent transverse and vertical sections of same. 

 2 knd 3. Tangential and vertical sections of a fragment of the var. senilis (see p. 127), , 



showing the great abundance of the median tubuli and the structure of one ol the 



solid spots. 

 4 and 5. Tangential and vertical sections of a well preserved and typical example. 



6. Small portion of a transverse section prepared from the same specimen that furnished 



the originals of flgs. 1 and 12. 



12. Vertical section of a thick specimen. (See flgs. 1 and 6). Only one side of the zoarium 



is entirely represented. 



13. Tangential section of a young example. 



For the external characters of this species see plate VII. 

 Middle third of the Trenton shales at Minneapolis and St. Paul. 



Figs, 7 and 8. Ehinidictta fidelis Ulr 134 



7. Tangential section, showing structure immediately beneath the surface; 7a, small por- 



tion of same section showing appearances at the bottom of the vestibular region; 76, 

 another portion of same, showing the form of the primitive portion of the zocecia and 

 the minutely tubular character of the walls and mesial laminse. 



8. Vertical section of same specimen, showing well developed superior hemisepta. 

 Middle third of the Trenton shales at Minneapolis. 



Figs. 9 to 11. EUETDICTTA MULTIPORA Hall (?) 139 



Tangential, transverse, and vertical sections of a narrow frond from the upper third of 

 the Trenton shales at St. Paul. (See also plates VII and XIV.) 



Figs. 14 to 18. Rhinidictta teentonensis Ulr 135 



14 and 15. Transverse and vertical sections of a young example. 



16 and 17. Vertical and tangential sections of a thicker specimen. In this each side is in 



part composed of two distinct layers of zocecia. 

 18. Primitive or prostrate portion of one zooecium of flg. 16, more highly magnified (X50). 

 See also plate VII. 

 Lower third of the Trenton shales, Minneapolis, Minn. 



Figs. 19 and 20. Rhinidictta gbandis, n. sp 136 



Vertical and tangential sections of a specimen from the "Lower Blue" limestone at 

 Dixon, 111. 



