CORALS AND CORALLIFORM TYPES. 41 



entirely destitute ol' iuterual structures, or coutainiug in the great ma,jority ol' cases : (1) 

 well developed tabula^ with or without radiating septa ; or (2), vesicular tissue with or 

 without tabultE and septa ; or (3) a distinctly hexamerous or tetramerous system of septa ; 

 or (4) indications of bilateral symmetry. 



The class, as thus defined, may be subdivided provisionally, and especially for deter- 

 minative purposes, into eight leading sections, as in the following scheme : 



Oorallite cell entirely empty, i.e., without any internal structures : 



S^ 1. Vacuata (Type form, Aulopora.) 



Septa absent or quite rudimentary ; tabula^ well developed : 



§ 2. Tabuiata (Type form, Favosites.) 

 Corallites united by a tubular or cellular cœueuchyme. 



§ 3. Cellulata (Type form, Fistulipora.) 

 Tabixlœ and septa both present. 



§ 4. Tabulo-Stellata (Type forms, Amplexus, Zaphrentis.) 



Tabuhe central only, surrounded by area of vesicular tissue. Septa well 

 developed : 



§ 5. Vesiculo-Stellata (Type forms, CyalhophyUum, Lonsdalia) 



Tabulfe entirely replaced by irregular vesicular tissue : 



§ 6. Vesiculosa (Type form, Cystiphyllum.) 



Cell provided with an operculum composed of a single valve or of several valves : 



S^ Y. 0PERCUL.4.TA (Type form, Calceola.) 

 Cup or cell containing septa only ; tabulae absent : 



§ 8. Integri-Stellata (Type form, Pelraia.) 



§ 1. Vacuata : — The representatives of this section, distinguished essentially by their 

 tubular cells being entirely destitute of internal structures, are of very doubtful position. 

 Very probably, they should be referred to the Alcyonaria or placed near the Sertularians 

 under the Hydro-medusœ ; but nothing deiinite, it is obvious, can be determined on this 

 point, and as the forms in question are of not uncommon occurrence in palaeozoic strata, 

 it has been thought advisable to retain them here, at least provisionally. They form but 

 one family, that of the Atdopondœ, containing the following genera : 



Fam. Auloporidœ : — Corallum composed of short, tubular or funnel-shaped empty 

 cells, united in branching groups : 



Sec. IV., 1892. U. _ 



