. [5 ,o f 

 INTRODUCTION. 



HP HIS book, like the rest of the series, is intended as an 

 -*- introductory working manual for the collector, the object 

 of its analytical tables being to enable him to name any specimen 

 in the British list without reading more than is needful for that 

 one purpose. It is on the same principle as its predecessors. In 

 the Flowers we dealt with a natural kingdom ; in the Birds with 

 a natural class, in the Butterflies and Moths with a natural order ; 

 in this volume we are dealing with a natural sub-kingdom, so that 

 we have had an example of each of the four highest systematic 

 groups treated on the same plan. 



Every living species of the sub-kingdom generally claimed as 

 a native of our country is here sufficiently described to distinguish 

 it from the rest, whether it has a shell or not ; thus rather a wider 

 range is covered than the main title would indicate, as many of 

 the mollusca do not have shells. The coloured plates include all 

 the species having shells, and these are drawn the size of life or 

 enlarged in the case of those too small to be clearly shown and 

 then their natural dimensions are given alongside. 



Of those without shells a representative of each genus is figured. 

 The sea-slugs are given in colour, and are either of the natural 

 size or enlarged. The cuttle-fishes are illustrated in two full-page 

 plates, but it need hardly be said have had to be reduced ; indeed 

 it would have been difficult to draw them to full scale, particularly 

 if we had followed the lead of one enthusiast and included Archi- 

 Uuthls among the British genera, on the strength of the specimen 

 captured off the Irish coast which had tentacles thirty feet long, 

 mandibles four inches across, and eyes fifteen inches in diameter. 



There is no species of the mollusca solely British except perhaps 

 Limntza, involuta, which comes from a pool on the Cromagaun 

 mountain, near Killarney, and is consequently Irish ; but even this 

 is regarded by some as a variety. The other land species occur 



