285 ZOANTHARIA. 



drical corallites are united together by horizontal connecting-processes of 

 an exothecal nature. 



Lastly, a natural transition is effected between the typical Cyatho- 

 phyllids and the typical Zaphrentidce by means of such genera as 



Fig. 166. — Structure of Lithostrotion Martini, from the Carboniferous Limestone, a, Trans- 

 verse section, enlarged about 2V2 times ; b, Vertical section, similarly enlarged. h, Cardinal 

 septum, situated in the fossula ; g, Counter septum ; js, Alar septa : co, Columella ; e, Vesicular 

 tissue ; t, Tabulae. (Original.) 





Omphyma and Campophyllum. The genus Omphyma is wholly confined 

 to the Silurian rocks, and comprises simple, turbinate or cylindro-conical 

 corals, the wall of which gives out root-like processes of attachment of an 

 exothecal nature (fig. 167, a). The calice shows four shallow fossulae, 



placed at right angles 

 a - to one another, and 



lodging the four lead- 

 ing septa ; and the 

 same structure is 

 shown in transverse 

 sections of the cor- 

 allum (fig. 159, a). 

 The septa are nu- 

 merous, and are al- 

 ternately long and 

 short ; but even the 

 longest septa extend 

 a limited distance 

 only into the visceral 

 chamber, thus leav- 

 ing a very extensive 

 central area, which 

 is occupied by the 

 tabulae (fig. 159, b). 

 The genus agrees in 

 this respect with the 

 Zaphrentoids, but it 

 shows its relation- 

 ship with Cyathophyllum by the possession of an external zone of ves- 

 icular tissue, though this is comparatively of small thickness, and is 



Fig. 167. — Omphyma subturbinata, from the Silurian of Gotland, 

 reduced in size, a, Side view of the corallum : b, View of the calice 

 showing the four fossulse. (After Milne-Edwards and Haime.) 



