Since that time eight or ten distinct genera of Labyrinthodonts have been discovered in the Carboniferous rocks of England, Scotland, and Ireland, not to mention the American forms described by Principal Dawson and Professor Cope.

The analytical habit of mind which finds vent in the subdivision of species, is also exhibited in a tendency to break up large genera into a number of small ones, but in the present group this practice has the disadvantage of obscuring a broad distinction between the dominant types inhabiting respectively the old world and the new.

The two highest groups of the Annulosa, the Insecta and the Arachnida, are represented in the Coal, either by existing genera, or by forms differing from existing genera in quite minor peculiarities.

And in this case, as also in our own character, it will be in our power to run over all kinds of argumentation separately: and at one time to refer all separate genera to different classes of the division, and at another to ask of the hearer what he requires, and at another to adopt a similar course by a comparison of one's own arguments and those of the opposite party.

Like all the genera above named, it appears to be peculiar to Australia.

That they have diverged greatly is obvious from the manner in which species of all kinds can be classed under genera, genera under families, families under sub-orders and so on; and I can remember the very spot in the road, while riding in my carriage, that, to my joy, the solution occurred to me; and this was long after I had come to Down.

Latreille has done the same for the Crustacea and Insects; and Milne Edwards, with the coöperation of Haime, has recently proceeded upon the same principle in characterizing a great number of Genera among the Corals.

Taking the practice of the ablest naturalists in discriminating Genera as a guide in our estimation of their true nature, we must, nevertheless, remember that even now, while their classifications of the more comprehensive groups usually agree, they differ greatly in their limitation of Genera, so that the Genera of some authors correspond to the Families of others, and vice versa.

But as the parts of the organism are governed and held together by the soul, so individuals are joined with one another into species and genera by higher unities.