280 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 
however, of the grasshoppers (Grylline Sw.) retain 
their colours very well ; and they never vary in the same 
species. The colour and patterns of shells, particularly 
those of the marine tribes, afford very good specific 
distinctions ; for, upon the whole, they seldom vary to 
any great extent. When we except two or three species 
of olives (Oliva Lam.), a few land shells, and the tellin 
bivalves ( Telline) we specify the chief, if not the only, 
exceptions to the universality of this observation. It 
must be understood, however, that no dependence can 
be placed upon the presence or the number of bands, 
which often cross the whorls both of the land and the 
marine genera: these, and the precise pattern of the 
markings, will often vary in the same species ; of which 
the common garden snail is a noted example. The pat- 
tern, also, of the angular zigzag markings, seen on the 
bat ‘volutes * and pier aesiel species forming the 
genus Cymbiola, are scarcely alike in two individuals out 
of twenty, although the general style of these markings 
will be precisely the same. Passing from these few 
exceptions, the cowries may be cited as a group of shells 
remarkable for the specific uniformity of their colours : 
indeed, but for this, so slight are their modifications of 
form, that there are many species which we should find 
it difficult to distinguish in any other way. 
(341.) There are other ‘remarkable ways in which 
colours vary among insects, of which the student should 
be apprised. In numerous species of the Chrysomelide, 
golden green is the prevalent hue; yet varieties of each 
are often found of a rich green blue, or of a greenish 
gold colour. The brilliant American Eumolpi fre- 
quently exhibit these variations, among individuals ob- 
viously of the same species. Most of all, the saltatorial 
Galleruci of tropical America, when alive, have a large 
proportion of pure white about them ; yet when they 
die, and as they are seen in cabinets, these parts appear 
of a light ochre or dull yellow colour. Some of the small 
light-coloured Casside of the same region are still more 
* See Cymbiola Vespertilio, Zool. Ill. ser. ii. pl. 83. 
