have the metatarsus more robust and its trochleæ more expanded than those from Glenmark. The representatives of Mesopteryx casuarina at Enfield have the tibia about 17.5in. long, while in those from Hamilton it averages 18.25in. These instances are sufficient to show that the species are not more restricted than is necessary for convenience of description. If they were made larger we must either use a cumbersome system of sub-varieties; or else, by clubbing varieties together, lose all chance of solving our problems. No one, I presume, at the present day would refuse to recognise two species because intermediate links had been found. This is a pre-Darwinian idea, which means that before a group of individuals may be allowed to form a distinct species all the steps of the ladder on which it rose must be destroyed. This would be a very hard rule for the palæontologist to obey, for he would have to examine and classify the mutations by which one species changed into another without being allowed to give distinct names to any of them. The difficulties involved in making a correct classification of the moas are due partly to the gradation of characters during the long interval between the earliest and latest forms known: partly to their extraordinary number, through which bones belonging to some three or four genera and ten or twelve species are usually found mixed together: and partly to collectors who either do not preserve intact individual skeletons or, what is much worse, add a bone or two to make a skeleton more complete. These difficulties are so great that the task of straightening things out appears almost hopeless. Nevertheless they must be faced if the problems I have mentioned are to be solved; and we can only hope that by constantly correcting our mistakes they may in time gradually disappear, and we shall then be able to write the remarkable history of the development of the moas in New Zealand in considerable detail, and with considerable confidence that we are giving a fairly-true representation of what really took place. Descriptions of New Species. Dinornis strenuus. This species contains all the birds from the South Island which have, up to now, been included in D. struthioides. I formerly thought that the differences between the birds of the two Islands were not sufficient to separate them; but I find that those from the South Island have constantly the metatarsus more robust, and with more widely diverging trochleæ than those from the North Island. In D. strenuus also the tibia is rather shorter and more robust than in D. struthioides. These differences—which will be seen in the following table—when combined with a difference in geo-