Question: Who wrote the 40th and final title in the regular series of Oz books, illustrated by Dick Martin in 1963?
Context: The Land of Ev is a fictional country in the Oz books of L. Frank Baum and his successors.  Its exact location is unclear between text and maps. " The Road to Oz" states that Ev is to the north of the Land of Oz, and in "Ozma of Oz", Princess Ozma of Oz and her procession enter the Munchkin Country and meet the King of the Munchkins upon leaving the palace at Evna, the capital city.  Subsequent books place Ev nearer to the Winkie Country, and the map on the endpapers of "Tik-Tok of Oz" shows the Munchkin Country as having no northern border with the desert that surrounds Oz, as a thin strip of the Gillikin Country extends even farther east than most of the Munchkin Country.  This map depicts Ev as a small country to the northwest (the compass rose is reversed) of Oz, with the Dominions of the Nome King as a separate area.  James E. Haff and Dick Martin's map, following the text, place the Nome Kingdom under an Ev that takes up the entire portion allotted to the Nome King's dominions on Baum's map. Yankee in Oz is a 1972 Oz novel by Ruth Plumly Thompson.  It was the first published by The International Wizard of Oz Club.  A letter from the Henry Regnery Company, which bought Reilly & Lee, is reproduced in the front indicating the publisher's blessing for the new Oz book to appear.  It was originally written in 1959, but because the Oz books were not selling, it was not published.  The first two editions of the book were published in 8½ x 11 inch format and running only 94 pages.  This was done at the request of illustrator Dick Martin to reduce the number of required illustrations and to show them closer to the actual size they were drawn.  The second printing (1986) featured a new cover, with the first edition artwork reprinted preceding the title page.  The third printing (2007) is standard Oz book size.  Its cover is a gaudier redesign of the second edition cover.  The book also features maps by James E. Haff, and as such, Thompson correctly places the Winkie Country in the west of Oz. The Enchanted Island of Oz is a children's novel written by Ruth Plumly Thompson and illustrated by Dick Martin, and first published in 1976.  As its title indicates, the book is an entry in the series of Oz books created by L. Frank Baum and his successors.  It is the last (and shortest) of Thompson's 21 novels about the Land of Oz. The Forbidden Fountain of Oz is a 1980 children's novel written by Eloise Jarvis McGraw and her daughter Lauren Lynn Mcgraw (or McGraw Wagner), and illustrated by Dick Martin.  As its title indicates, the book is one entry in the long-running series of Oz books written by L. Frank Baum and his many successors. The Marvelous Land of Oz: Being an Account of the Further Adventures of the Scarecrow and the Tin Woodman, commonly shortened to The Land of Oz, published on July 5, 1904 , is the second of L. Frank Baum's books set in the Land of Oz, and the sequel to "The Wonderful Wizard of Oz" (1900).  This and the next 34 Oz books of the famous 40 were illustrated by John R. Neill.  The book was made into an episode of "The Shirley Temple Show" in 1960, and into a Canada/Japan co-produced animated series of the same name in 1986.  It was also adapted in comic book form by Marvel Comics, with the first issue being released in November 2009.  Plot elements from "The Marvelous Land of Oz" are included in the 1985 Disney feature film "Return to Oz". This is a list of characters in the original sequel Oz books by American author L. Frank Baum, and in the later continued Oz series by his grandson Roger S. Baum, Ruth Plumly Thompson, John R. Neill, Jack Snow, Rachel Cosgrove Payes, Eloise Jarvis McGraw and Lauren McGraw, Dick Martin, Eric Shanower, and Sherwood Smith.  Characters from Gregory Maguire's "Wicked" are not included, as his works, among others such as the work of March Laumer, are considered "heretical" in Baum scholarship (The term "heretical" was first applied to these books by Dr. Stephen J. Teller of Pittsburg State University in the Winter 1988 issue of "The Baum Bugle" and appears regularly in Oz fandom). The Ozmapolitan of Oz is a 1986 novel written and illustrated by Dick Martin.  As its title indicates, the book is an entrant in the long-running series of stories on the Land of Oz written by L. Frank Baum and various successors. Dickinson P. Martin (June 29, 1927 – February 14, 1990) was an artist from Chicago who illustrated a number of books related to The Oz books series, most notably, "Merry Go Round in Oz" (1963), the 40th and final title in the regular series, as well as many other children's books. Merry Go Round in Oz (1963) is the fortieth in the series of Oz books created by L. Frank Baum and his successors.  It was written by Eloise Jarvis McGraw and Lauren McGraw Wagner (her married name was dropped from reprinted editions after the marriage ended).  It was illustrated by Dick Martin. The Oz books form a book series that begins with "The Wonderful Wizard of Oz" (1900) and relate the fictional history of the Land of Oz.  Oz was created by author L. Frank Baum, who went on to write fourteen full-length Oz books.  All of the Baum written books are in the public domain in the United States.  Even while he was alive, Baum was styled as "the Royal Historian of Oz" to emphasize the concept that Oz is an actual place.  The illusion created was that characters such as Dorothy and Princess Ozma related their adventures in Oz to Baum themselves, by means of wireless telegraph.
Answer: Eloise Jarvis McGraw and Lauren McGraw Wagner