PLATE L. 

 Fenestella oultrata. 



Page 120. 

 Fig. 1. A fragment, natural size, showing the manner of growth. 

 Fig. 2. A transvei'se section of the branches. (X (>.) 

 Fig. 3. A lateral view of a branch, showing a transverse section of the dissepiments, and the irregular 



ai-rangement of the cell apertures. 

 Fig. 4. A portion of the non-celluliferous face of a frond. (X 6.) 

 Fig. 5. A portion of the cellulifei-ous face. (X 6.) 



Upper Helderberg group. Ii\xlls of the Ohio river. 



Fenestella biseurulata. 



I'age 13d. 



Fig. 6. A fragment natural size, showing the manner of growth. 



Fig. 7. A transvei-se section, showing the form of the branches and carinse and the space occupied by 

 the cells. (X 6.) 



Fig. 8. A lateral view of a branch, showing a traiisvei'c section of the dissepiment"*, the cell apertures, 

  the crennlations in the margin of the carina, immediately above and corresponding in iiumbei' 

 to the cell apertures. The projections on the side of the carina have somewhat the appear- 

 ance of a range of minute cells, but the lithographic figure does not propei-ly represent the 

 original drawing. (X 6.) 



Fig. 9. A portion of the non-celluliferous face of a frond, Showing the comparative size and character of 

 the branches and dis-sepimentM. (X 6.) 



Fig. 10. A portion of the celluliferous face, showing the cell apertures and also the expanded summits of 

 the cariu* with their lateral crennlations. The lithogi-aphic figure has failed to preserve the 

 effect of the original di'awing ; the same criticism will apply to tig. 11. 



Fig, 11. An enlargement of a portion of the celluliferous face, having the carinas broken away, leaving 

 the branch grooved along it« center, showing the form and arrangement of the cell apertures, 

 and theii' elevated margin.-* slightly indenting the borders of the fenestrules. (X ti.) 

 Upper Uelilerberg group. Palh uf the Oh'ui river. 



Fenkstella UKAMFKKA. 

 Page \a. 



Fig. 12. An enlargement of a portion of the non-celluliferous face, showing angular sinuous branches \vith 

 dissepiments much wider than the branches. (X 6.) 



Fig. 13. An enlargement of a {>ortion of the non-celluliferous face, showing flattened branches and dissepi- 

 ments, with a row of minute granules along the middle of the branch. The flattened branches 

 and dissepiments would indicate that the specimen has been woni or mac§i'ated, but in that 

 case it seems hanlly jxissible that the granules should be so well preserved. 



Pig. 14. An enlargement of the celluliferous face of a portion of the frond from near the base, covered by 

 an organic deposit, which forms a solid crust over that portion of the specimen. 



Fig. 16. A portion of the non-celluliferoua face enlarged to six diametere ; the left side of the figure shows 

 two branches in the same conditions as those of fig. 13 ; the two adjacent branches are apjiar- 

 ently woi-n so that the cells are partially exposed ; the right of the figure shows the branches 

 broken away so that the under sides of the expanded crenulate carinse are exposed. 

 Upper Helderberg group. Near Le Roy, N. Y. 



