XIV. 



SUCCESSION OF LIFE-FORMS. 



403 



AFFINITIES OF OOLITIC TKIGONI^E. 



pectinata. 



dsedalea. 



alaeformis. 



*navis. 



*Goldfussii. 



*lineata. 



Trigoniae, transversely-ribbed or ornamented with transverse 

 rows of tubercles, mark two conspicuous fossil groups, neither of 

 them paralleled in modern nature. The modern species is radiated 

 from the beak, and so is T. Goldfussii of Alberti, found in the 

 muschelkalk. Each of the groups seems to begin in the trias ; only 

 one of them survives ; the two most abundant races are exclusively 

 fossil. We seem here to behold a group capable of striking 

 variation at one and that the earliest epoch, and of long continuing 

 perseverance in the differences then occasioned. 



* The species thus marked are not British. That named T. Goldfussii by Albertj 

 is a shell of the Keuper and muschelkalk ; the same name is given by Agassis to 

 a very different oolitic form. 



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