302 OUR COMMON BRITISH FOSSILS. 



ends of knowledge. Not much more than a quarter 

 of a century ago, conchologists were careful only to 

 collect shells ; they hardly cared for the a'eattires to 

 whom those shells originally belonged, and many 

 knew very little of their life-histories, now the most 

 valuable part of them. 



Whatever may be the actual zoological position of 

 the Cephalopoda (to which these Orthoceratitcs, Ammo- 



Fig. 300. — Exterior of Shell of Pearly Nautilus (recent). 



nites^ Belemnites, etc., belong), there is no question 

 that they stand at the head of the Mollusca. This 

 is evident from their high organization, their well- 

 developed eyes, nervous and muscular systems, hydro- 

 static apparatus, etc. Thanks to our public aquaria, 

 most people are acquainted with the appearance of 



