Je) 
i | 
PACE: ON THE COLUMBELLID. 
at the British Museum, and by his continual readiness to assist with 
his kindly advice and valuable critical opinion, has placed me under 
an obligation which I can never hope to be able to repay. ‘To 
Mr. C. Hedley I am in many ways indebted, and more particularly for 
the sacrifice of time and trouble by which a recent short stay in Sydney 
was rendered one of my most pleasant reminiscences: with Mr. R. 
Etheridge, jun., and the authorities of the Australian Museum, I have 
also to thank him for facilities for working at the ‘‘ British Museum 
of the Antipodes.” My thanks are due to Dr. G. Pfeffer and the 
authorities of the Hamburg Museum for the loan of a large series of 
specimens and for granting me most exceptional facilities for working 
at that institution. Through the kindness of Mr. J. H. Ponsonby 
I have been enabled to see an extensive collection of the South African 
forms.. Mr. D. J. Adcock, Mr. J7 H. Gatliff, and Dr. J. C. Verco have 
furnished me with much Australian material. The late M. Hervier 
submitted his collection of Lifu Columbellide to me, though I was 
unfortunately not able to work at them. Mr. J. C. Melvill kindly 
permitted me to examine the whole of the material, collected by 
Mr. F. W. Townsend in the Persian Gulf, that he subsequently 
described in collaboration with Mr. R. Standen. Mr. H. B. Preston, 
Mr. H. Fulton, and Mr. G. B. Sowerby have assisted me to obtain 
specimens; and Mr. C. Davies Sherborn, Mr B. B. Woodward, and 
Mr. E. R. Sykes have afforded me much help in the solution of knotty 
points of bibliography. ‘To these, and to many others, too numerous 
for individual mention, who have given or lent me material or who 
have in other ways rendered me kindly assistance, I would return 
my most grateful thanks. 
Some General Remarks.—The question ‘‘ What is a ‘species’ ?” 
is one which at the present time admits of no very satisfactory reply ; 
and to answer it becomes more and more diflicult the greater the 
bulk of the material studied. When only a few specimens are before 
one it is an easy matter, in the case of the Mollusca, as with other 
groups, to divide these up into more or less natural ‘species.’ To 
do the same, however, when dealing with large series of examples, 
which have been collected at different localities, frequently becomes 
a most difficult problem, and in certain groups it would even seem 
an insoluble one. ‘This is really only what might be expected; for 
the publication of the ‘‘ Origin of Species,’ and the research carried 
on since Darwin wrote his epoch-making work, have rendered the 
idea of ‘species’ in the Linnean sense quite untenable. However, 
this fact, though long since recognized by the morphologists, has 
as yet hardly made itself felt among systematic malacologists. 
That some change must be made in our eonception of species! 
is certain; but it is as yet by no means so evident in what 
1 Where, in the following pages and in future papers, the word ‘species’ is used, 
it must be regarded merely as a convenient term to denote an assemblage otf 
individuals occurring at the same station, whose variations one into another 
so graduate that they form a continuous series; and it must not be taken 
as implying any views as to the genetic aflinities of such assemblage. 
