SYKES : CONCMOLOGV AT i:)A\VN ANl) CLOSfi OF NINETEENTH CENTURY. 39 



needed ; at present there is but little certainty as to hoAv far back the 

 actual species of our marine fauna may be traced, the views of Jeffreys 

 and Searles Wood, the only two authors who in this country have 

 given special attention to the question, being in direct conflict. 



Another problem which lies still before us, and needs far more know- 

 ledge than we at present possess for its solution, is as to the effect of 

 surroundings upon molluscan life in the production of marked and 

 persistent variations. Take for example some of the Achatinellce which 

 are found as commonly sinistral as dextral. The cause of this is yet 

 to seek ; it has been, however, suggested that sinistral specimens of 

 MelaiitJio are due to crowding in the embryonic stages. Again, how 

 can we explain the occurrence in one particular locality of specimens 

 of Buccinuiii undatum having two, and even three, opercula ? There 

 is, therefore, no lack of questions which invite study from the w^orker 

 of the present day. 



Looking back, we realize that the past hundred years have been 

 times in which descriptive work has flourished ; often it is to be feared 

 at the expense of accuracy and deeper research. The advances made 

 in our knowledge of anatomy bear no comparison to the study of the 

 shelP; much, too, is it to be regretted that the zeal of authors for the 

 describing of novelties has again and again caused them to rush into 

 print without a sufficiently careful study of the works of their prede- 

 cessors, and their successors will have no light task before them. 



The close of the nineteenth century is, to use a commercial expres- 

 sion, a time to " take stock," and to consider what progress has been 

 made. It is with one of these forms of estimating our present position 

 that I propose for a few minutes to concern myself, and specially with 

 an endeavour to arrive at some idea ot the actual number of species 

 of recent mollusca which are now known to science. Any such esti- 

 mate can but be approximate, but a survey of the most recent 

 monographs enables one to form a fairly accurate conception. 



The classic starting-point for such a calculation, as indeed for all 

 other systematic molluscan work, is the tenth edition of Linnaeus' 

 " Systema Naturae." His "Vermes Testacea" number 703, but he 

 includes Serpula and other non-molluscan genera, while his "Vermes 

 Mollusca," of which, again, only a portion are really molluscs, are 69. 

 Roughly speaking, therefore, the known species of mollusca at this 

 date were about 700. After this the steady influx of newly-described 

 species gradually increases the number nearly every year ; JVIiiller, for 

 example, in 1773, admits 398 land and freshwater forms. Steadily the 

 exploration of new countries added to the catalogues, and Dillwyn in 



I Mr. M. F. Woodward : " I can only impress on all collectors abroad the desirability of pre- 

 serving the animals as well as the shells, not merely of their new finds, but of the commonest 

 forms, hardly any of which are properly known." 



