2 INTRODUCTION. 
SIZE OF FIGURES. 
Where there is no ‘‘size-line” the figures may be taken as the 
natural size, except in the case of the three largest bivalves, which, for 
convenience sake, are figured smaller than the average size of adult 
specimens. In these cases I have stated their dimensions besides the 
figures and also in the descriptions. 
I have used millimetres for measurements, except for the mussels 
where it would have been absurd, and for the slugs, which latter are 
understood to be measured, fully extended, from the nose to the 
extremity of the keel. 
TRANSLATION OF NAMES AND GLOSSARY OF TERMS. 
I have translated and accented the names of the genera, species and 
varieties, and have appended a glossary of all the technical terms which 
I have been compelled touse. Dr. Jeffreys points out that it may be a 
guide to some to remember that in the pronunciation of names ending 
in -zzas those derived from the names of animals usually have the 
penultimate syllable long, as they are formed from the Latin 
{Neritina, anatina, etc.) ; while those words which have a similar 
termination, but are derived from the names of vegetable or mineral 
substances (Achdtina, crystallinus, etc.) being derived from the Greek, 
have the penultimate short. It may also be remembered that the 
long and the short syllables in the classics are in fact the accented and 
unaccented syllables respectively. 
PLATES AND DESCRIPTIONS INSUFFICENT FOR 
IDENTIFICATION. 
It should be borne in mind that plates and descriptions are at 
best but a second-rate substitute for a direct examination of the objects 
themselves, and that more may be done towards the identification of 
difficult species by a careful comparison with a good collection of well 
authenticated specimens than by working with plates and descriptions 
alone. 
