PLATE XI. 



Fig. I. Transverse section of a few of tlie tubes of Halysiies catenularia, Linn., 

 from the Wenlock Limestone of Dormington, Stoke-Edith, enlarged ten 

 times, showing the absence of septa in the large tubes, and the structure 

 of the intermediate tubes. The epitheca is left unshaded. 



Fig. I a. Part of a vertical section of another specimen of the same, from the 

 same locality, enlarged five times. The specimen is one in which the 

 tubes are of unusually large size, and the tabulae of the intermediate tubes 

 are subvesicular. 



Fig. 2. Portion of the surface of Thecia Swiudcrnana, Goldf , enlarged about 

 ten times. Wenlock Limestone, Dormington Quarry, Stoke-Edith. 



Fig. 2 a. Part of a transverse section of the same, enlarged ten times, showing 

 the obtuse septal ridges, the communication of the cavities of the polypes 

 by horizontal channels, and the filled-up tubuli of the interstitial tissue. 



Fig. 2 b. k. small part of the same transverse section, enlarged twenty times, 

 showing the filled-up interstitial tubuli. 



Fig. 2 c. Part of a vertical section of the same, enlarged ten times, showing the 

 tabulate larger corallites, the horizontal canals uniting the visceral cham- 

 bers of these, and the small tubules of the interstitial tissue. 



Fig. 2 d. Small portion of the same section, enlarged twenty times, showing the 

 interstitial tubuli. 



Fig. 3. Part of a transverse section of Fropora tid>i//afa, E. and H., enlarged 

 five times, from the Wenlock Limestone of Dudley. The specimen is one 

 in which the septa are unusually small and short. 



Fig. 3 a. Part of the same section, enlarged ten times. 



Fig. 3 b. Part of a vertical section of the same specimen, enlarged ten times. 



Fig. 4. Portion of the surface of an altered specimen of Lyellia glabra, E. and 

 H., from the Upper Silurian of Iowa, of the natural size (copied from 

 Edwards and Haime). 



Fig. 4 a. Portion of a specimen oi Lyellia glabra, E. and H., seen from one 

 side, enlarged (copied from Edwards and Haime). 



Fio-. 5. Part of a tangential section oi Plasmopora petaliformis, E. and H., from 

 the Wenlock Limestone of Gotland, enlarged five times. 



