CHAPTER IV 

 PRESENT HISTORY AND DISTRIBUTION 



WITH such a past history as just recorded, it is 

 little wonder that the Mollusca both have 

 been and are abundant. 



In 1866 a rough estimate gave the number of 

 extinct species as 18,568, and living ones as 20,502. 

 The list has been considerably extended since that 

 time, and though no further estimate of the fossil 

 forms appears to have been attempted, a recent cal- 

 culation puts the number of living species known at 

 the end of last century at upwards of 50,000. This 

 total may be distributed among the five classes as 

 follows : Amphineura, 600 ; Gastropoda, 40,100 ; 

 Scaphopoda, 230 ; Pelecypoda, 8,600 ; Cephalopoda, 

 470. 



Naturally, too, so ancient and so numerous a race 

 is widely distributed over the surface of the globe 

 to-day, and its members have become adapted to 

 very varied conditions of life. The majority are 

 marine, and mostly confined to the littoral and 



5i 



