The present work is intended to appeal to two kinds of readers to the field-naturalist, who, while interested in life-histories, habits, and geographical distribution, beauty or strange-ness of forms, is indifferent to the homologies of the metasternum or similar questions ; and to the morphologist, who in his turn is liable to forget that his specimens were once alive. A great portion of the book is anatomical and systematic. It was necessary to treat anatomy, especially that of the skeleton, somewhat fully, since it has long been recognised that it is impossible to base a scientific classification upon external characters. The reader familiar with Vertebrate anatomy has a right to expect that questions of special morphological interest will be dwelt upon at length. Those who have no anatomical foundation must be referred to one of the now numerous introductory manuals on the subject.