xiv INTRODUCTION. 



as an appropriate introduction to the descriptive details 

 that follow. 



The Mollusca of the British seas are numerous and abun- 

 dant. The varied conformation of the coasts of Great 

 Britain and Ireland, and of the sea-bed surrounding these 

 islands, is peculiarly favourable for the nourishment of a 

 multiplicity of kinds of these animals. The climatal con- 

 ditions of our area are such as to encourage the presence 

 and perpetuation of both northern and southern temperate 

 types, and the influence of very difl'erent ancient conditions 

 is manifested by the presence among them of not a few 

 shell-fish of boreal or arctic origin. Our Mollusca are, 

 when taken collectively, not remarkable for brilliancy of 

 painting, magnitude of dimensions, or singularity of con- 

 tour ; although in all these respects we can boast of 

 striking exceptions, and among our minute species can 

 show many of exquisite elegance and curious sculpture. 

 By far the larger part of our marine Mollusks are tiny 

 species. Our uudibranchs are, however, distinguished for 

 the beauty of their colouring, and even among the despised 

 ascidians there are some whose coats are tinged with the 

 brightest or else the most delicate hues. The cuttle-fishes 

 that live around us are too excursive and oceanic in their 

 habits to be claimed as exclusively, or even chiefly, our own. 

 Those that frequent our sea-bed are mostly animals of con- 

 siderable size for Mollusca, and certainly among the most 

 astonishing and beautiful of the inhabitants of the sea. 

 They are, however, seldom seen by the casual observer, 

 whose knowledge of our Molluscan treasures is mainly 

 derived from sorry specimens of shells, cast upon the sea- 

 beach by the waves. 



The land-shells of the British islands are still less striking 

 than the testacea of the surrounding seas. Their hues 



