552 A. J. Slieanhy — On Operculate Corals. 



beautifully preserved small undescribed species of Tryplasma and 

 Cyathophyllum, which also possess remains of delicate anchoring 

 stolons, points to the existence of quieter waters, probably in the 

 shape of a lagoon or harbour free from the violence of heavy seas. 



EXPLANATIOX OF PLATE XXVI. 

 Figs. 1-18 : Upper Silurian operculate corals from Hatton's Corner, Yass, N.S.W. : 

 Fig. Rhizophyllum robust xm, Shearsby. 



1 . Dorsal view. 



2. Ventral view, showing fossula, septa, and vesicular tissue. 



3. Lateral view. 



4. Calice, showing fossula and calicinal bud. 



5. Apical \aew. 



6. Part of ventral surface, showing vesicular tissue. X 2. 



BhizophyUum yassense, Shearsby. 



7. Outline of vertical median section. 



Rhizophyllum australe, Eth. fil. 



8. Lateral view. 



Rhizophyllum interpuHctatum, De Kon. 



9. Lateral view with operculum in situ. 



10. Apical view. 



11. Dorsal view with operculum in situ. 



12. Operculum, inner surface showing median ridge with pit-like depression. 



12a. Operculum, inner surface showing median ridge and radiating granular lateral 

 ridges. 



13. Ventral view of specimen with calicinal bud. 

 H. Lateral ,, ,, 



15. Dorsal ,, ,, 



16. Another specimen, ventral view showing calicinal bud, and remains of two 



exothecal processes (?) . 



17. Dorsal view of an almost complete specimen with operculum in situ and widely 



opened, showing median ridge and radiating lateral ridges of operculum, and 

 the counter septum and septa of the ventral wall. 



18. Lateral view of same specimen, showing projecting nature of median ridge of 



the operculum. 



d = dorsal surface, v = ventral surface. 

 Note.- — Fig. 6 is twice natm'al size ; all the other figures are drawn natural size. 



Figs. 19-2.5 : Upper Silurian operculate corals showing exothecal processes, from 



DerrenguUen Creek, Yass, N.S.W. : — 

 Fig. 



19. Rhizophyllum robustuni, Shearsby. Ventral view showing remains of rootlets, 



and abnormal growth of calicinal bud. 



20. R. interpunctatum, De Kon. Dorsal view of budding form, showing one 



rootlet on the small parent form and four on the bud. The bud also shows 

 a strong counter septum. 



21. R. interpunctatum. Ventral view shomng three .strong rootlets at the lateral 



angle and one near the middle of the ventral surface. 



22. R. interpunctatum. Lateral view showing rootlets. 



23. R. australe, Eth. til. Lateral A'iew with lateral and median rootlets on the 



ventral surface, and also one on the dorsal surface. 



24. R. australe. Ventral view with lateral and median processes, and one near the 



middle of the ventral margin. 



25. R. interpunctatum (?). Dorsal view of specimen showing four rootlets. 



Note. — Figs. 19-25 are slightly magnified. 



