To a sub-class selected for a centre, two qualities are indispensably requisite. They have been previously given from Mr. MacLeay, who, it will be remembered, discovered that one of each of his five groups contained types of the other four, besides a type peculiar to itself. This quality must hold good in any group thus selected for a centre; it must contain types of the six surrounding groups in the first place. Now, is this applicable to Papilio? Have we not already experienced the greatest difficulty in finding three good approaches, the smallest number which a sub-class can possess? How then can we hope, by any good fortune in discovery, to make ourselves masters of three other entirely new ones, and these to sub-classes to which it is confessedly the most unlike? Phalæna, on the contrary, presents us with Lasiocampa, Ægeria, Cilix, Lithosia, Apatela and Orgyia, five of which genera beautifully typify the approximating sub-classes. The preference on this score then is decidedly with Phalæna. The second position, that it should contain a type peculiar to itself, is almost a matter of course; but my own idea is, that the very centre should not only be a type of the genus, or order, or sub-class, but of the class itself of which it is the centre. From this position, then, a further and still more important question arises,--What is the type of Lepidoptera? The parts which afford the generic characters of Lepidoptera, and, I believe, generic characters in the perfect state are the only ones of any value, are these--the mouth, palpi, antennæ and wings; and, as no medium can constitute a type, the excess of these characters, whether superlatively or diminutively considered, must be resorted to as the most probable means we possess of discovering what this type may really be. First, then, the mouth. In Lepidoptera, we find two distinct characters in this;--first, its entire absence; secondly, its being furnished with prodigiously long antlia. The first character is that of Phalæna, the second that of Sphinx. Next, the palpi are either entirely obsolete or exceedingly prominent, the first in Phalæna, the second in Pyralis. Thirdly, the antennæ are remarkably pectinated, or clavated, or setaceous: the first character is that of Phalæna, the second that of Papilio, the third that of Noctua. Fourthly, the wings are enormously expansive in proportion to the body, or remarkably small,--the first is the character of Phalæna, the second that of Sphinx. It need scarcely be added, that all these characters are to be met with in every intermediate degree of intensity. Now, it appears, that Phalæna possesses an extreme of each of the four principal characters, Sphinx of two, Noctua of one, and Papilio of one; therefore Phalæna is the typical genus, Phalænæ the typical order, and Phalæna the typical sub-class of Lepidoptera: and a necessary conclusion from this fact is, the type of Lepidoptera is an insect without antlia or palpi, with