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LETTER VII. 



OBSERVATIONS ON TURBINATED MADREPORITES CONTINUED 



PORPITAL OR SHIRT-BUTTON MADREPORITE SYNONYMA 



MADREPORES NOT FOUND IN A MINERALIZED STATE. 



JH.ARDLY any of the animalized parts of creation are arranged with 

 more difficulty than those remains of zoophytes which are obtained 

 in a fossil state. The labours of the little creatures by which they 

 have been modelled, frequently appear as if they had been capri- 

 ciously and sportfully performed; deviations from their ordinary 

 model, apparently unnecessary, being frequently to be observed. The 

 avoiding, perhaps, of some little obstacle to their labours, the repair- 

 ing of some little injury, which accident may have occasioned to their 

 operations ; or many other circumstances, not to be ascertained, may 

 have occasioned these departures from the usual mode in which they 

 had been wont to execute their assigned task. Hence the substances 

 which they have formed may possess such anamolies of form, as may 

 render it difficult to determine whether they should be considered as 

 specific characteristics, or only as such accidental modifications of the 

 structure of a species as give rise to varieties. The difficulty of making 

 the necessary distinction, in these cases, must necessarily be much 

 greater when, as is frequently the case with fossil specimens, we are 

 deprived of the advantage of comparison, by having only one specimen 

 on which to exercise our judgment. Especially since it also often 

 happens, that its characteristic marks have been, in a great measure, 

 effaced by the injuries to which it has been exposed, during a period 

 of several thousand years. 



