CCELENTERATA : RUGOSA. 175 



strong argument against this view is to be found in the fact 

 that the typical Rugose corals possess well-developed septa 

 structures which, if they do not absolutely imply the existence 



Fig. 88. Calceola sandalina. 

 Fig. 87. Strombodes pentagomis. An operculate Rugose Coral. 



A Silurian Rugose Coral. Devonian. 



of mesenteries^ are, at any rate, unknown in any living Hydro- 

 zoon. At present it is not possible to speak definitely as to the 

 systematic position of the Rugosa, but they appear to form a 

 natural and distinct group, intermediate in many respects be- 

 tween the Zoantharia and the Alcyonaria. 



The Rugosa are divided into the following families : 



1. STAURID.<E : Septa well developed, extending from the bottom to the 



top of the visceral chamber, and showing a conspicuous quaternary 

 arrangement. Dissepiments are present, and there is a central 

 tabulate area. Genera Stauria, Polycoelia^ Metriophyllum, Holo- 

 cystis, Conosmilia. 



2. CYATHAXONID^E : Corallum simple, with a deep calice ; septa well 



developed, the four primary septa not predominantly developed ; no 

 dissepiments or tabulae. Genera Cyathaxonia, Guynia, Haplo- 

 phyllia. 



3. CYATHOPHYLLID^ : Corallum simple or compound ; septa well de- 



veloped, but not so completely so as in the two preceding groups ; 

 the four primitive septa not pre-eminently developed ; tabulse always, 

 and dissepiments generally, present. Genera Zaphrentis y Amplex- 

 tis, Cyathophyllum, Heliophyllum, Omphyma^ Lithostrotion, Lons- 

 daleia, Clisiophyllutn, &c. 



4. CYSTIPHYLLID^ : Corallum simple or rarely compound ; wall com- 



plete ; septa rudimentary ; visceral chamber with small convex 

 vesicles formed by a combination of tabulae and dissepiments; 

 sometimes an operculum. Genera Cystiphyllum, Goniophyllum, 

 Rhizophyllurn, Calceola. 



