It is the Magic Tree House 41th book.
The 3rd book in the Magic Tree House series is "Magic Tree House #3: Mummies in the Morning".
The 20th book in the Magic Tree House series is Dingoes at Dinnertime.
The 44th Magic Tree House book is A Ghost Tale for Christmas Time and it was published in 2010.
Magic Tree House book #39 is called "Dark Day in the Deep Sea".
The very last Magic Tree House book in the series is "Hurricane Heroes in Texas" which is book number 135.
Magic Tree House #48 Saturday in a Snowstorm Magic Tree House #49 Midday in a Mayan Kingdom Magic Tree House #50 Autumn in Ancient Egypt Magic Tree House #51 August in Arabia Magic Tree House #52 Riding Chariots in Rome
The newest Magic Tree House Book is Dogs In The Dead Of Night which is coming out in August 2011.---- As of for June 2011 the day I am writing this answer, the newest Magic Tree House book is book #45-A Crazy Day With Cobras.
It is a book that has a brother and sister travel to different times via Morgan Le Fay's magic tree house (morgan is not evil in this book).
Yes, there is a book 46 in the Magic Tree House it's name is Dogs In The Dead Of Night.
There is no "Magic Tree House Island."The 19th Poptropica island is called Red Dragon Island,loosely based on book 37 in the Magic Tree House book series.(see the related question)
The 41st book of the Magic Tree House series was published on March 10, 2009.