FOSSIL CORALS. 67 



corals, whose surface breaks out here and there into 

 flower-like calyces, and whose tips usually terminate in 

 the same sort of objects. The entire structure is dis- 

 tinguished by its light and porous character — whence 

 the name of the group. In spite of their apparent 

 fragility, we find them living amid the most violent 

 of seas, for their rapid growth enables them to 

 withstand the destructive effects which would other- 

 wise break them up. The division Aporosa did not 



Fig. 50. — Astrcea rotiilosa, a recent West Indian compound Coral. 



make its appearance in Primeval seas, but is first 

 observed in strata of the Secondary period, although 

 its species are most abundant in the present epoch. 

 The Perforata are feebly represented among primary 

 fossils by Silurian and Devonian genera, such as 

 Protarca and PlcurodidyunL Perhaps the modern 

 Perforata are better known by their common name of 

 Madrepores. 



