536 TABULAR VIEW. 



It is evident that the genera Echinus, Balanus, Bucardia, Area, Nu- 

 culus. Modiolus, Pinna, Auricula, Plicatula, Lima, PateUa, and Nautilus, 

 which are found in the most ancient and in the recent strata, as well 

 as in our seas, in the living state, must have traversed the chalk, and 

 their debris would have been found there if their soluble testa had not 

 disappeared. 



The genera found in all the strata, chalk inclusive, as well as in the 

 living state, are eight in number : viz. Caryophyllus, Seriatopora, 

 Serpula, Mitylus, Pecten, Ostrea, Terebratula, and Tupia. As to the 

 last, however, it has been rarely found in the chalk. 



In the foregoing list we have given all the principal genera found fossil, 

 excepting only those of which some doubt appeared to exist ; as to the 

 species, we have purposely avoided an enumeration of them, for the 

 obvious reason that the progress of discovery renders it impossible to 

 set limits to their number, any more than to those of the living species. 



*^* In our tabular view of the fossil genera of invertebrata, the ascend- 

 ing order is pursued, as most convenient. 



