TAB. XII. 

 CORALS FROM THE PORTLAND STONE. 

 ISASTREA OBLONGA (p. 73). 



Fig. 1 . A fragment silicified ; natural size. 



1 a. Calices (natural size), showing the different modifications produced by fossili- 

 zation and wear; in some of the corallites the interseptal loculi are filled up 

 with a calcareous deposit. 



1 ^. A horizontal section, natural size, showing the well-preserved corallites. 



1 c. A portion of the same section magnified. 



1 d, 1 e. Horizontal section of a portion of the corallum that is partly silicified and 

 partly filled up with calcareous matter. The gray parts are those in which 

 the silex has replaced the tissue of the walls and the septa ; the white radii 

 correspond to the loculi of the visceral cavity, occupied by the calcareous 

 deposit. In fig. 1 e this deposit having been effected in an intermittent 

 manner has produced the appearance of large pali. 



1 /. A vertical section of a portion of one corallite, showing the thick simple walls, 

 the dissepiments, the granulated siu-face of the septa, their denticulate inner 

 edge, &c. 



