Plate 28. 



Figs. 1-12. Tretoq/rloccin lorlUi.i Lonsdalo, 184.5. (p. 206.) 



I, 2. Fragments of the irres,'ularly branched, cylindrical zoarium, natural size. 



3. Surface of a specimen, X 12, with a group of broken ovicells. Tlie superior layer of the ovicells 

 has disappeared in fossilization. 



4. A large isolated ovicell, X 12, with its upper surface broken away. 



5. Surface of ordinary zooecia, X 12, showing the mesopores grouped together iu many parts of 

 the branch. 



6. Same surface, X 25, illustrating the thickness of the zooecial walls. 



7. 8. Another surface, X 12 and a portion of the same, X 25, in which the zooecia have thin walls 

 and the mesopores are aiTanged irregularly between the apertures. 



9. Outer portion of longitudinal thin section, X 25. 



10. Tangential thin section, X 26. 



II. Several zooecia of the same, X 100, showing that the internal walls are much calcified and 

 are separated by a less dense tissue. 



12. Portion of a transverse thin section, X 25. 

 Miocene (Yorktown formation): Yorktown, Virginia. 

 272 



