RUGOSA. 213 



to the forms which are really to be included under this head, 

 and if the typical members of the genus are destitute of 

 tabulae and dissepiments, it must then be rather referred to 

 the Turbinolidce. In the genus Amplexus, which ranges from 

 the Silurian to the Carboniferous, the structure of the coral- 

 lum is essentially similar to that of Zaphrentis, but the septa 

 are much less developed, and are so short as to leave the 

 central portion of the tabulae smooth and bare. In Loplio- 

 phyllum, of the Devonian and Carboniferous, the corallum 

 essentially resembles Zaphrentis; but there is a flattened 

 columella. In the Devonian Anisophyllum, again, there are 

 three septa pre-eminently developed (fig. 100, B and c), and 

 in Hallia (also Devonian), there is one such predominant 

 septum, towards which a number of the septa are inclined. 

 Lastly, in the Silurian Streptelasma, the tabulae are less 

 developed than in Zaphrentis, and some of the septa are pro- 

 longed inwards to the centre of the visceral chamber in the 

 form of twisted plates. 



In the Cyathophyllince, in the second place, the septa are 

 more or less regularly radiate in their arrangement (fig. 106), 



Fig. 106. A, Cross-section of Heliophyllum Halli, of the natural size Devonian ; B, Cross- 

 section of a fragment of Cyathophyllum regium, of the natural size Carboniferous. 



and there is often no septal fossula. The corallum may be 

 simple or compound, the tabulae are confined to a more or 

 less extensive central area, and there is often an external 

 zone of vesicular tissue formed by the great development of 

 the dissepiments in this region. 



