CHAPTER XXII. 
AN OUTLINE OF THE GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA. 
The Mollusca being for the most part marine, it does not enter 
into the plan of this work to go into much detail as to their 
distribution. The orders and families will, however, be passed 
briefly in review, and all terrestrial and fresh-water groups 
discussed in somewhat more detail ; with the object of showing 
how far their distribution accords with that of the higher 
animals, and to what extent the anomalies they present can be 
explained by peculiarities of organisation and habits. If the 
views advocated in our fifth chapter are correct, the regions 
there marked out must apply to all classes of animals ; and it 
will be the task of the students of each group, to work out in 
detail the causes which have led to any special features of 
distribution. All I can hope to do here, is to show, generally 
and tentatively, that such a mode of treatment is possible ; and 
that it is not necessary, as it is certainly not convenient or 
instructive, to have a distinct set of “ Regions ” established 'for 
each class or order in the Animal and Vegetable Kingdoms. 
For all the Marine groups I have merely summarised the 
information contained in Mr. Woodward’s Manual of the 
Mollusca , but in the case of the Land Shells I have consulted 
the most recent general works, and endeavoured to give an 
accurate, though doubtless a very incomplete, account of the 
most interesting facts in their distribution. As their classifica- 
tion is very unsettled, I have followed that of the two latest 
great works, by Martens and Pfeiffer. 
