4. Apaturidæ.—Of this we have only one representative—the Purple Emperor ([Plate V], fig. 1).
5. Satyridæ.—Including the 'Browns' and 'Heaths,' and numbering eleven species.
6. Lycænidæ.—Including the Hairstreaks, 'Coppers,' and 'Blues,' in all seventeen species.
7. Erycinidæ.—Containing only the 'Duke of Burgundy.'
8. Hesperiidæ.—This family contains seven British butterflies commonly known as the 'Skippers.'
Although all the members of the same family resemble each other in certain points of structure, or in their habits, yet we can often find among them a smaller group differing from all the others in one or two minor particulars. Such smaller groups are called Genera.
To make this all quite clear we will take an example.
The Brimstone Butterfly ([Plate II], fig. 4) belongs to the second family—Pieridæ, all the members of which are distinguished from those of the other families by the characteristics mentioned on [page 141].
But our Brimstone Butterfly possesses another very prominent feature in which it differs from all the other British Pieridæ, and that is the conspicuous projecting angles of both fore and hind wings. Among the foreign species of the family we are considering there are several that possess these angles; but as there are no others among our own members, the 'Brimstone' is placed by itself in the list of British Lepidoptera as the only member of the genus Gonopteryx or 'angle-winged' butterflies.
Thus the full relationship of this butterfly to other insects may be shown in the following manner: