TAB. XVII. 



CORALS FROM THE CORAL RAG. 



Thamnastrea arachnoides (p. 97). 



Fig. 1 . Side view of an adult specimen ; natural size. 



1 a. A young specimen ; natural size. 



1 d. Calicular surface of a young specimen, slightly magnified, 



1 c. Side view of a young specimen, the growth of which has been intermittent. 



1 d. Calices magnified. 



1 e. Variety having the calices disposed in almost parallel series, and placed at a 

 greater distance than usual ; natural size. 



If. Some of the calices of this last variety, magnified. 



1 ^. A specimen much weather-worn, in which the terminal portion of the calices 

 has disappeared and the walls have become prominent ; natural size. 



1 /i. Some well-preserved costae, magnified. 



1 i. Some weather-worn costse, magnified. 



Ij. A specimen the calicular surface of which is slightly worn down ; natural size. 



1 i-. A specimen much modified by the process of fossilization ; natural size. 



