CHASTER : SPECIES AND VARIATION. 3I 



that I agree with the process of multiplying species, that seems to be 

 going on. Its disadvantages will be evident if I narrate an ex- 

 perience of my own. Some years ago I was so fortunate as to 

 receive a considerable number of bags containing dredgings and anchor 

 mud from many parts of the Mediterranean, Adriatic, and ^gean 

 seas. Amongst the small mollusca obtained from these were 

 thousands of specimens of TurbonillcE. of the T. lactea group. In 

 sorting out this assemblage of shells it was at first quite easy to 

 select specimens which agreed perfectly with typical examples of named 

 species. But very soon this became increasingly difficult: a specimen 

 would turn up which closely resembled some species, whilst pre- 

 senting indications of a character not possessed by that species but 

 by some other. There was always a great residuum of shells that it 

 was utterly impossible to allocate. I may add that the Marquis of 

 Monterosato, the greatest authority on the Mediterranean mollusca, 

 once sent me a number of shells of the same group with a letter 

 asking me to attempt to separate them into species. In such a 

 group as this which we find widely distributed and very variable the 

 logical or most scientific procedure seems to be to treat it as a 

 species with a number of varieties. The varieties need not be very 

 closely and rigidly limited. We thus permit of a separation and 

 division of specimens sufficiently accurate for practical purposes. If 

 we keep to a partition into species we can scarcely call a shell 

 Ttirbonilla acutissiina which might almost as well be classed with 

 T. delicatula. But if we class all as T. lactea and note how, as we 

 extend the area of our observations, the shell shows signs of varietal 

 modification in different ways, we are gaining an insight into the 

 influence of environmental conditions, which is of distinct value. 

 I open a book almost at random and find such a remark as 

 this upon the distinctive characters of a new species of Succinea : — 



"Allied to 5. and S. . From the latter it is quite 



recognizable, being of a warmer colour and less produced spire." 

 Or, again, concerning a new Claiisilia we read :• — " The single 

 specimen is not in very good condition. It is a somewhat 

 more slender shell than C. and is noteworthy for its con- 

 tracted and elongate mouth, \vhich has quite a different appearance. 

 The plicae palatales in this species too, are more nearly equal 



than in C. in which the first is much the largest. The 



specimen was picked out from amongst a number of C. " Now 



I do not desire to mention the author's names, for our literature is 

 being flooded with just such descriptions. Nor do I dispute the 

 possibility of these forms eventually proving good species. What I 

 wish to emphasize is that no pains have apparently been taken to 

 learn the range of variability of the forms from which these novelties 



