THE GRAPTOLITES AND CORALS 311 



simple, with a lamina from cardinal to counter-septum 

 running through the false columella. 



GROUP : Cystiphylloidea. Simple ; with great de- 

 velopment of dissepiments, replacing tabulae and leading 

 to degeneration of the septa. Includes the only corals 

 with an operculum to the calyx. Genera : Cystiphyllum 

 (Sil.-Dev.), cylindro-conical, no operculum ; Goniophyllum 

 (Sil.), four-sided pyramidal, with an operculum of four 

 pieces; Calceola (Dev., Fig. 94, ^), slipper shaped, with 

 an operculum of one piece. 



The post- Palaeozoic Madreporaria are sometimes 

 united as Hexacoralla. The order of development of the 

 septa in them differs greatly from that of Rugosa. They 

 are usually divided into three orders (or sub-orders), 

 though it is now very doubtful if these express natural 

 affinities. 



SUB-ORDERS : Aporosa. Theca and septa compact. 

 Include two principal families. 



Family Tuvbinolidce. Without dissepiments. Simple. 

 Genera : TiwUnolia (Eoc.-Rec.), conical, with projecting 

 lamella and very prominent costae ; Smilotrochus, similar 

 but no columella ; Fldbellum (Eoc.-Rec.), compressed, 

 calyx elliptical, costae weak. 



Family Astvceidce. With dissepiments; simple or 

 compound. Includes the chief reef-building corals. 

 Genera : (i) Simple Parasmilia (Cret), already described; 

 Montlivaltia^ (Jur.-Cainozoic), conical, turbinate or dis- 

 coidal, no columella, dissepiments abundant, covered 

 externally by a perishable calcareous skin (epithccd). 

 (2) Compound Thecosmilia (Jur.-Cain., Fig. 94, ^), 

 essentially a Montlivaltia, which becomes compound by 

 equal fission ; Isastraa (Trias.-Cret, Fig. 94, /), massive, 

 with prismatic corallites ; Holocystis (Lower Cret., Fig. 

 94, g), massive, remarkable for superficial resemblance 

 to some Rugosa, there being four septa longer than the 

 others, and tabulae being well developed. 



