300 



ZOANTHARIA. 



commonly more or less angulated, and assuming a pyramidal or 

 quadrilateral figure. Internally, the structure may not differ essen- 

 tially from that of Cystiphyllum, the visceral chamber being filled 



with an endothecal vesicular 

 TiT/77?^-^ - tissue, and the septa being in- 



complete or rudimentary (fig. 

 182, b). Sometimes the septa 

 are obsolete, but they are usu- 

 ally recognisable as radiating 

 ridges or rows of tubercles in 

 the calice, or they may even 

 form radiating lamellae which 

 intersect the marginal region of 

 the visceral chamber. The 

 essential character of the family, 

 however, is found in the fact 

 that the calice is closed by a 

 variously constructed lid or 

 " operculum," composed of one 

 or more pieces (fig. 182, a). 

 In this feature, the corals of 

 the present family differ from 

 all recent Madreporarians, 

 though a species of operculum 

 is found in some living Al- 

 cyonarians {Primnoa and Par- 

 amuriced). The structure and 

 affinities of the family of the 

 Operculate Corals have been 

 admirably worked out by Lind- 

 strom ; and all the known 

 genera of the family are Silu- 

 rian or Devonian. 



In the Silurian Go7iiophyllum 

 (fig. 182) the corallum is distinctly 

 quadrilateral, its four sides being 

 flattened. The internal structure 

 is wholly vesicular, the cells of the 

 central region of the visceral 

 chamber being of large size and 

 representing tabulae. The quad- 

 rangular calice is deep, and is furnished with marked septal ridges, of 

 which four — one in the middle of each side — are specially prominent, 

 the longest being the " cardinal septum," while the other three are the 

 " counter " and " alar " septa. The septa are not mere calicine striae, but 

 are truly lamellar, though they are marginal. The calice is closed with 



Fig. 181. — Cystiphyllum vesiculosum, showing 

 "rejuvenescence," the corallum consisting of a 

 succession of cups produced by budding from the 

 original polype. One side of the calice is broken 

 away, and shows the internal structure. Of the 

 natural size. Devonian, America and Europe. 

 (Original.) 



