CHAPTER IV 
PRESENT HISTORY AND DISTRIBUTION 
W ITH 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 
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 
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