GENERAL CHARACTERS. 
3 2 5 
Noxious Molluscs. 
thrushes, and other birds; by lizards, toads, snakes, and even by certain kinds of 
carnivorous insects. The fresh-water forms are consumed in vast quantities by 
water-birds of every description, by fishes, frogs, water-voles, and other mammals, 
and aquatic creatures of various kinds; and every seashore is constantly ransacked 
by flocks of sea-fowl for the repasts of shell-fish it affords. Out in the depths 
of the ocean many kinds of fishes, especially cod, haddock, gurnard, soles, and 
mullet, are great devourers of molluscs, which ever fall a prey, not only to one 
another, but also to crabs, holothurians, sea-anemones, and star-fishes; and, finally, 
among the pelagic pteropods the Greenland whale seeks his daily sustenance. 
Molluscs of all kinds, but especially the marine species, are much eaten by the 
natives of most countries; and even in Europe, although the oyster is the most 
highly appreciated, several other species are used as food. Molluscs are not only 
of importance to man as an article of diet, but they are serviceable in other ways. 
Their shells are employed as personal ornaments, and are used in the manufacture 
of fishing-tackle by some uncivilised people. In England and other countries 
many of the pearly species are manufactured into ornaments and various useful 
articles, and the beautiful pearls themselves, secreted within the tissues of the 
pearl-oyster, are esteemed as jewels. 
The utility of the molluscs to man probably far outweighs the 
injury which is occasioned by a few kinds. In the foremost rank of 
the noxious species stands the Teredo, the great destroyer of submerged timber. 
The damage done to piers, boat-bottoms, and in fact to wood of any description 
which is located in the sea, is enormous, and there seems to be no effectual means 
of meeting the attack of these molluscs, except by covering the timber with metal¬ 
sheeting. The stone - work of breakwaters occasionally becomes more or less 
damaged by the burrowing habits of the Pholas and Saxicava. On land, snails 
and slugs commit onslaughts upon our crops and gardens, but these pests are more 
easily overcome than their marine relatives. 
Although this is a subject very fascinating to some, it is one 
which pre-eminently opens the gates of speculation. That species 
have certain geographical and bathymetrical limits in their distribution, may be 
an admissible fact in very many cases, but when the reason for this limitation is 
sought we are reminded how little we know of natural causes. That certain tracts 
of coast have their own peculiar inhabitants, and that the molluscs of the eastern 
shores of America, for example, differ from those of the west we must admit; but 
how this has come about, is matter of conjecture. We say that differences of 
environment, of food and temperature, are sufficient reasons to account for such 
things. On the contrary, we are met with the fact that certain species in a given 
genus have a much wider range than others, and we are fain to ask how this is 
Distribution. 
brought about. 
The rano’e of terrestrial molluscs is much more restricted than 
C5 
that of most marine forms. This is readily understood, as the means of dispersal 
are very different. The early stages of marine molluscs, if not free-swimming 
creatures, are liable to be carried great distances by ocean currents, or the action of 
the tides and wind. On the contrary, land-molluscs are creatures of slow progres¬ 
sion, and are liable to have their distribution hindered, either by rivers, mountains, 
or seas. Consequently we find that island faunas, as regards the terrestrial species, 
