44 Land and Freshwater Mollusks. 



animal life on the globe, is perhaps, the greatest triumph to which 

 a naturalist can aspire. Many theories have been formed, many 

 ingenious conjectures advanced, but the truth is not yet known: 

 whatever that truth may be, speculations respecting centres of 

 creation, variations of species, or development will cease or be 

 verified when the great fundamental law — if indeed there be such 

 —is known and proved. 



To aid in any degree towards such a discovery, it is obvious 

 that the accurate observation and recording of facts is of the first 

 necessity, and it has always appeared to me that facts respecting 

 the comparatively minute and seemingly insignificant animals of 

 which we now speak are, for this purpose, peculiarly valuable. 

 These creatures are small, often minute, they therefore may longer 

 escape dangers and the extinction which overtake more bulky 

 animals; the food of each species is for the most part abundant 

 and readily procurable ; they are little exposed to ihe interference 

 of man, partly from their insignificant size, partly from their not sup- 

 plying his obvious wants — 1 speak strictly of land and freshwater 

 mollusks ; they are of low organization, therefore their tenacity 

 of life and power of repairing injury is great ; on the other hand 

 their powers of increase are not remai'kable, and they do not 

 thei'efore spread rapidly or widely ; their powei'S of adaptation to 

 new conditions of climate or food, do not as far as we know seem 

 great ; lastly, their means of locomotion are extremely limited, 

 and in the case of the land shells, can scarcely be aided by the 

 accidents of life of uncivilized man, or by the habits and move- 

 ments of the lower animals. 



These considerations and others, make observations on the 

 distribution of land shells very interesting and most valuable to 

 the naturalist, who looks eagerly to the attainment of the wider 

 truths of his science. It is obvious, therefore, that a gain to general 

 knowledge, material in fact for the attainment or verification of 

 some discovery, results from the publication of any accurate and 

 fairly exhaustive local list. Interesting facts immediately show 

 themselves during the progress of the work; for example, the 

 small and beautiful little shell Azeca tridens which, without being 

 rare, is at least local, was known in the north-east of England and 

 across to the south west, but a list for the neighbourhood of 

 Sevenoaks, Kent, published some years ago, records its existence 

 there, the spot indeed is curiously confined, and there seems to be 

 but one locality in the whole district ; it has since been found also 

 in Surrey. Again, the largest of our species of Clausilia is very 

 local, I have only procured it in England in one place, the bank of 

 the Thames, beyond Hammersmith, mentioned as a locality by 

 Gray ; the curious Testacella, a slug with a small external shell — 



