PLATE XVIII. 



Fig. 1. — Vertical section of Clathrodictyon variolar e, Rosen, enlarged 10 — 12 

 times. From a specimen from the Silurian Limestones (zone of Pentamerus 

 esthonus) Kattentack, Esthonia. (Page 150.) 



Fig. 2. — Tangential section of the type specimen of the same species enlarged 

 10 — 12 times, from the Silurian Rocks of Errinal, Esthonia, from a fragment 

 presented to the author by Magister Friedrich Schmidt. 



Fig. 3. — Vertical section of the preceding, similarly enlarged. 



Fig. 4. — Vertical section of a variety of Olathrodictyon variolare, Rosen, from 

 the Wenlock Limestone of Dormington, enlarged 10—12 times. 



Fig. 5. — Tangential section of the preceding specimen, similarly enlarged. 

 The section traverses one of the astrorhizse. 



Fig. 6. — Vertical section of Clathrodictyon crassum, Nich., from the Wenlock 

 Limestone of Ironbridge, enlarged 10 — 12 times. (Page 151.) 



Fig. 7. — Tangential section of the preceding specimen, similarly enlarged. 



Fig. 8. — Half of a specimen of Clathrodictyon regulate, Rosen, from the 

 Wenlock Limestone of Dudley of the natural size. (Page 155.) 



Fig. 9. — Portion of the surface of the same, similarly enlarged. 



Fig. 10. — Vertical section of the same, enlarged 10 — 12 times. 



Fig. ]0 a. — Small portion of the preceding, enlarged 22 times. 



Fig. 11. — Tangential section of the same, enlarged 10 — 12 times. 



Fig. 1 1 a. — Small portion of the preceding, enlarged about 22 times. 



Fig. 12. — Under surface of a small specimen of Clathrodictyon vesiculosum, 

 Nich. and Mur., from the Wenlock Limestone of Dudley, of the natural size. The 

 missing half of the specimen is restored in outline. (Page 147.) 



Fig. 13. — Clathrodictyon confertum, Nich., Middle Devonian, Dartington. 

 Vertical section, enlarged 10 — 12 times. From a specimen presented to the author 

 by Mr. Champernowne. (Page 154.) 



Fig. 14. — Tangential section of the same, similarly enlarged. 



