PLATE VIII. 



PAGE. 



Figs. 1 to 3. RHINIDICTYA MUTABILIS Ulr 125 



Three portions of an old example of this species *9, showing, in 1, the thick, rounded 

 and granulose margin, in 2, the shape of the zooecial apertures at the upper extremity 

 of the specimen, and In 3, their form near the lower end of same. (See also plates 

 VI and VII.) 



Figs. 4 and 5. PACHYDICTYA PUMII/A Ulr 157 



Two fragments of the natural size, and one of them representing the basal part of the 

 zoarium, xg. (See also plate X, and remarks on p. 158.) 



Figs. 6 to 10. RHINIDICTYA EXIGUA Ulr 131 



6 and 7. The basal part of a specimen of the natural size and X9. One of the branches has 

 three, the rest of the zoarium four rows of zocecia. 



8. A delicate fragment with only three rows of zooecia, 



9 and 10. A branching fragment of the natural size and the lower half xg, This has from 



five to seven rows of apertures. 

 Lower third of the Trenton shales at Minneapolis. 



Figs. 11 to 17. PACHYDICTYA ACUTA (Hall) and varieties 155 



Figs. 11 and 12. A specimen of the natural size and a portion xg. Trenton limestone, 



Trenton Falls, N. Y. 



13. A very small specimen, with only six and seven rows of zooecia, from the Galena lime- 

 stone near Fountain, Minn. 

 14 to 16. Three specimens from the Galena shales near Cannon Falls, Minn. 



17. Surface, xg, of a well preserved fragment from the same horizon and locality as the pre- 



ceding. (See also plate IX.) 

 Figs. 18 and 19. PACHYDICTYA EL.EGANS, n. sp 154 



18. A very nearly perfect zoarium of this species, natural size, from the lower part of the 



Galena shales at St. Paul. Later collections show that this species is exceedingly 

 abundant at that locality and that the specimen here figured divides with greater 

 frequency than usual. 



19. Enlargement of the beautifully ornamented surface of same, xis. (See also plate IX.) 

 Figs. 20 to 27. PACHYDICTYA OCCIDENTALS Ulr 151 



20 to 24. Five specimens of the natural size, illustrating the variable character of thezoaria. 

 25. Surface of flg. 24, xg. 



26 and 27. A frond of the natural size and a portion of its surface xg, traversed by irregular 

 grooves caused by interruptions in the development of the zooecia. (See also plate IX.) 

 Upper third of the Trenton shales at St. Paul. 



Figs. 28 to 34. PACHYDICTYA FIMBRIATA Ulr 152 



28 to 30. Three specimens of the natural size, the last one the widest seen. 

 31 and 32. A very narrow and seemingly young example, natural size and the upper part xg. 

 33 and 34. An excellently preserved fragment of the natural size and a portion xg. This pre- 

 sents the fully matured condition of the species. (See also plate IX.) 

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



