PLATE XX. 



Fig. 1. — Vertical section of a specimen of LabecMa conferta, Lonsd. sp., from 

 the Wenlock Limestone of Dudley, enlarged about 10 times. 



Fig. 2. — Tangential section of the same specimen, similai^ly enlarged. 



Fig. 3. — Small portion of the preceding section, enlarged about 30 times. 



Fig. 4. — Upper surface of a specimen of LabecMa scabiosa, Nich., from the 

 Wenlock Limestone of Dudley, of the natural size. 



Fig. 5. — Under surface of the same, of the naturalsize. 



Fig. 6. — Surface-tubercles of LabecMa scabiosa, enlarged. 



Fig. 7. — Portion of a polished slab of LabecMa stylophora, Nich., from the 

 Middle Devonian of Shaldon, Devonshire, of the natural size. 



Fig. 8. — A single cylinder of the same transversely divided, enlarged 5 times. 



Fig. 9. — Vertical section of LabecMa canadensis, Nich. and Mur. (?), from the 

 Ordovician Rocks of Aldons, near Girvan, enlarged 10 times. Collected by Mrs. 

 Robert Gray. 



Fig. 10. — Polished slab of Stromahrpora concentrica, Goldf., cut vertically to 

 the surface, of the natural size. From the Middle Devonian, Lummaton, Devon- 

 shire. 



Fig. 11. — Tangential section of a specimen of Stromatopora concentrica, Goldf., 

 from the Middle Devonian of Lummaton, Devonshire, enlarged 10 times. 



Fig. 12. — Vertical section of a specimen of Stromatopora concentrica, Goldf., 

 from the Middle Devonian of Teignmouth, enlarged 10 times. 



