Some words in this text are found in both hyphenated and non-hyphenated form (for instance: Condylo-basilar/condylobasilar, mid-winter/midwinter). These variations match the text of the original document. A few obvious punctuation errors have been repaired. Spelling has been retained as it appears in the original publication, except as follows: p. 372, in "A more homogeneous vegetation would tend to pass" homogenous has been changed to homogeneous. p. 415, "1953. Foods, and dens of the opossum ..." has been changed to "1953. Food and dens of the opossum ..." In Fig. 11 the bottommost y-axis label in the scale of gms. is probably an error: 45 should be 35. Some illustrations have been moved from their original locations to paragraph breaks, so as to be nearer to their corresponding text, and for ease of document navigation. References to scale in illustration captions are those of the original publication, and therefore do not correspond to the scale of the images in the HTML version of this ebook. The list of University of Kansas Publications from the front of the original document has been joined to its mate at the end of this text. Because the cover of the original document contained text exactly duplicated on the title page, this cover information has been omitted.