552 



GEOLOGY 



the organ-pipe coral (Syringopora, b) ; and the cup coral (Zaphren- 

 tis, e). A most peculiar coral of the simple class (Goniophyllum, //) 

 was quadrangular, and its top provided with a cover (operculum) 

 of four triangular plates hinged to the four sides of the cup's margin. 



if?iV-.*-*t?fV'V 



' I ^M*?' 



Fig. 403. Silurian Corals and Bryozoans: a-e are corals, a, Favosites occi- 

 dens Whit.; 6, Syringopora verticillata Goldf.; c, Halysites catemdatut 

 Linn.; d. Goniophyllum pyramidale (His.); e, Zaphrentis tinthonuta 

 Homing. Bryozoans, / and g, Fenestdla parvulipora Hall. 



When closed they formed a pyramid over the cup (d, Fig. 403, only 

 two of the opercular plates shown). This was a protective device 

 unknown among modern corals. 



With their increase in abundance, the corals acquired the hal>it 

 of associating themselves together. This resulted in the formation 

 of reefs. The known reefs appear to have been formed some 



