Even in the Carboniferous period, though land plants abound, air-breathers are not numerous, and most of them have only been recently recognised. We know, however, with certainty that the dark and luxuriant forests of the coal period were not destitute of animal life. Reptiles[122] crept under their shade, land snails and millipedes fed on the rank leaves and decaying vegetable matter, and insects flitted through the air of the sunnier spots. Great interest attaches to these creatures; perhaps the first-born species in some of their respective types, and certainly belonging to one of the oldest land faunas, and presenting prototypes of future forms equally interesting to the geologist and the zoologist. [122] I shall use the term reptile here in its broad, popular sense, as including Batrachians as well as reptiles proper. It has happened to the writer of these pages to have had some share in the finding of several of these ancient animals. The coal formation of Nova Scotia, so full in its development, so rich in fossil remains, and so well exposed in coast cliffs, has afforded admirable opportunities for such discoveries, which have been so far improved that at least twenty-five out of the not very large number of known Carboniferous land animals have been obtained from it.[123] The descriptions of these creatures, found at various times and at various places, are scattered through papers ranging in date from 1844 to 1891,[124] and are too fragmentary to give complete information respecting the structures of the animals, and their conditions of existence. [123] It appears that about a hundred species of Carboniferous reptiles have been recognised on the continent of Europe, in Great Britain, and in the United States. They belong to a number of distinct types, all, however, being of batrachian affinities. [124] Papers by Lyell, Owen, and the author, in the _Journal of the Geological Society of London_, i. ii. ix. x. xi. xvi. xvii. xviii.; "Acadian Geology," by the author; Papers in _Trans. Royal Society of London_, _Am. Jl. of Science_, and _Geological Magazine_. Footprints.