Thank you for your question, my name is ***** ***** need more information about the books. The full title, the author, the publisher, the condition and the type of binding (is it cloth, leather) and the condition.
The author William Temple Hornaday, Sc.D. was an American zoologist, conservationist, taxidermist, and author. He served as the first director of the New York Zoological Park, known today as the Bronx Zoo,
Your books are zoological in subject.
The Mentor Association published a variety of booklets they sell for $10.00 to $15.00.
The National Geographic Society books also sell for $10.00 to $15.00 each depending on the subject and condition. The Department of Natural History is possibly more. Is it possible to send an image of this book one of the whole book and one of the title page.