APOROSA. 



189 



same formation, should be looked upon as a tabulate form of 



the Astrceidce. By Prof. Martin Duncan, the Battcrsbyia of 



the Devonian, and the Heterophyllia of the Carboniferous, are 



considered old types of the Astrceidce. Lastly, some of the 



forms placed in the badly-characterised genus Petraia, of the 



Silurian and Devonian, may very probably turn out to be 



Turbinolidce, and this may possibly be the place of the 



Silurian Duncanella. 



The Aporosa are divided into the following families : 

 1. Turbinolidce. In this family the corallum may be 



simple or compound, but in the latter 



case it is without a cosnenchyma. The 



inter septal loculi are open from top to 



bottom, and are not crossed by dissepi- 



ments or synapticulse ; and the septa are 



mostly granulated on their sides. Leaving 



the doubtful ancient forms (Petraia and 



Duncanella) out of sight, the family makes 



its first certain appearance in the Lias 



(Thecocyathus). In the Cretaceous numer- 



ous forms are known, and in the Eocene 



Tertiary a still greater development of this 



type takes place, after which the family 



begins to decline in numbers to the pres- 



ent day. 



In Turlnnolia itself (fig. 75) the coral- 



lum is simple and conical, with a styliform 



columella, but without pali. The costae 



are very prominent, and the spaces be- 



tween them are marked with rows of 



small dimples, which look like perfora- 



.. . TIT i -i 11 i 



tlOnS 111 the Wall, but Which really do sulmta. The upper figure 



not penetrate to the visceral chamber. 



Turbinolia 



The genus is characteristic of the Eocene The lower fi ? ure 8hows 



, ~ the calice, with the col- 



penod. Flabellum, ranging from the LO- umella and primary and 



cene Tertiary to the present day, is nearly ^ dary septa " 

 allied to Turbinolia, but the corallum is 

 compressed, so as to produce an elliptic form of calice, and 

 the wall is covered with a thin epitheca. Caryophyllia, 



