39 



We shall now proceed to the examination of aggregated and undi- 

 vided madrepores, with distinct stars, and with porous and tuber- 

 culous ambulacra. Previously, however, to commencing this investi- 

 gation, it is proper to remark, that considerable difficulty frequently 

 occurs in the attempt to discriminate between the different madre- 

 pores of this class when fossil. This difficulty, which also sometimes 

 occurs in the class which has just been treated of, arises from the 

 circumstance of the superior surface of the coral, from which its spe- 

 cific characters are chiefly taken, being found covered over, and filled 

 up, with the extraneous matter, so as to be totally excluded from the 

 sight. In specimens of this kind, and which are by far most numerous, 

 no farther knowledge of the form of the coral can be obtained, than 

 what is discovered by sections of the specimen ; which being made 

 in different directions, yield information respecting the shape and 

 size of the stars, and the number and extent of their lamellae. But 

 as it is impossible thus to acquire any knowledge of the superior 

 surface of the madrepore, so an opportunity is seldom yielded for 

 acquiring information of the distance at which the stars are there 

 placed ; and never any respecting the peculiar characters of the lamella 

 or of the ambulacra. Hence permission must frequently be required, 

 in these cases, to substitute analogical inferences for actual observa- 

 tion and comparison. 



The figure given by Fougt,* as ma drepora favosa, represents a fossil 

 so much injured and altered, as renders it impossible to determine to 

 what species it belongs. 



The specimen figured Plate V. Fig. 9> bears a very strong re- 

 semblance, except that its cells are larger, to madrepora retepora. 

 The angulated cells are very similar ; but I have not been able, in the 

 fossil specimen, to detect the reteporous structure of the parietes of 

 the cells, which gives name to the recent madrepore. This, however, 



* Amcenit. Acad. Tom. I. Tab. IV. Fig. 16, 



