_The author expects to be taken to task for the use of scientific names, and the reader may perhaps sympathize with the old lady who said that the discovery of all these strange animals did not surprise her so much as the fact that anyone should know their names when they were found. The real trouble is that there are no common names for these animals. Then, too, people who call for easier names do not stop to reflect that, in many cases, the scientific names are no harder than others, simply less familiar, and, when domesticated, they cease to be hard: witness mammoth, elephant, rhinoceros, giraffe, boa constrictor, all of which are scientific names. And if, for example, we were to call the Hyracotherium a Hyrax beast it would not be a name, but a description, and not a bit more intelligible._ _Again, it is impossible to indicate the period at which these creatures lived without using the scientific term for it--Jurassic, Eocene, Pliocene, as the case may be--because there is no other way of doing it._ _Some readers will doubtless feel disappointed because they are not told how many years ago these animals lived. The question is often asked--How long ago did this or that animal live? But when the least estimate puts the age of the earth at only 10,000,000 years, while the longest makes it 6,000,000,000, it does seem as if it were hardly worth while to name any figures. Even when we get well toward the present period we find the time that has elapsed since the beginning of the Jurassic, when the Dinosaurs held carnival, variously put at from 15,000,000 to 6,000,000 years; while from the beginning of the Eocene, when the mammals began to gain the supremacy, until now, the figures vary from 3,000,000 to 5,000,000 years. So the question of age will be left for the reader to settle to his or her satisfaction._ _The restorations of extinct animals may be considered as giving as accurate representations of these creatures as it is possible to make; they were either drawn by Mr. Knight, whose name is guarantee that they are of the highest quality, or by Mr. Gleeson, with the aid of Mr. Knight's criticism. That they are infallibly correct is out of the question; for, as Dr. Woodward writes in the preface to "Extinct Monsters," "restorations are ever liable to emendation, and the present ... will certainly prove no exception to the rule." As a striking instance of this, it was found necessary at the last moment to change the figure of Hesperornis, the original life-like portrait proving to be incorrect in attitude, a fact that would have long escaped detection but for the Pan-American Exposition. The connection between the two is explained on page 76. However, the reader may rest assured that these restorations are infinitely more nearly correct than many figures of living animals that have appeared within the last twenty-five years, and are even now doing duty._