280 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 



however, of the grasshoppers (GryllmcB 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 ( TellijicB) 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 

 hat volutes * and other coronated 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 Chrysomelidce, 

 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 Cassidce of the same region are still more 



* See Cymbiola Fespertilio, Zool. Ill ser. ii. pL 83. 



