JSVIDENOE OF THE SILURIAN MOLLUSCS. 177 



EVIDENCE OF THE SILURIAN MOLLCTSOS 

 OF THE FOSSIL FLORA. 



A.NCIENT TKEE. 



After dwelling at such length on the earlier fishes, it may 

 seem scarce necessary to advert to their lower contemporaries 

 the mollusca, — that great division of the animal kingdom 

 which Cuvier places second in the descending order, in his 

 survey of the entire series, and first among the invertebrates, 

 and which Oken regards as the division out of which the im- 

 mediately preceding class of the vertebral animals have been 

 developed. " The fish," he says, " is to be viewed as a mussel, 

 from between whose shells a monstrous abdomen has grown 

 out." There is, however, a peculiarity in the moUuscan 

 group of the Silurian system, to which I must be permitted 

 briefly to refer, as, to employ the figure of Sterne, it presents 

 " two handles" of an essentially difierent kind, and, as in all 

 such two-handled cases, the mere special pleader is sure to 

 avail himself of only the handle which best suits his purpose 

 for the time. 



Cuvier's first and highest class of the mollusca is formed 

 of what are termed the Cephalopods, — a class of creatures 

 possessed of great freedom of motion : they can walk, swim, 

 and seize their prey ; they have what even the lowest fishes, 



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