302 OUR COMMON 1 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 creatures 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 Orthoceratites, 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 



