216 RUGOSA AND ALCYONARIA. 



phylline Corals, which are characteristically Carboniferous in 

 their range, and of which Clisiophyllum (fig. Ill, B) may be 

 taken as the central type. In the forms in question (Clisio- 

 pliyllum, Cydophyllum, Aidophyllum, Rlwdophyllum, &c.) the 

 structure of the corallum resembles that of the simple forms 

 of Cyathophyllum in the fact that there is a well-developed 

 exterior zone of vesicular tissue ; but the axis of the visceral 

 chamber is occupied by a series of more or less complicated 

 structures, which represent a modification of the tabulate 

 central area of Cyathophyllum, rather than a true columella. 



Fig. 111. A, Cross-section of two corallites of Lonsdaleia duplicata, Lower Carboniferous, 

 enlarged ; B, Cross-section of the corallum of Clisiophyllum Keyserlingi, Lower Carbonifer- 

 ous, of the natural size. (After James Thomson and the Author.) 



4. Cystiphyllidce. In this, the last and most aberrant 

 family of the Eugose Corals, the skeleton is usually simple, 

 though occasionally compound ; and the septa are rudimen- 

 tary, existing only as so many vertical striae or ridges within 

 the calice (fig. 112). The outer wall is complete, but the 

 entire visceral chamber is filled with small lenticular vesicles 

 formed by a combination of dissepiments and tabulae. A 

 distinct septal fossula is sometimes present. The family is 

 Palaeozoic, and is confined to the Silurian and Devonian 

 periods. 



In Cystiphyllum (fig. 112), the type-genus of the family, 

 the corallum is usually simple, and the vesicular tissue of 



