Hemingway's Cats: An Illustrated Biography
By Carlene Fredericka Brennen, Hilary Hemingway
(mentions family pet a white Yorkshire Terrier "Tassel")
http://books.google.com/books?id=yKFCgD0XN9EC&pg=PR16&vq=tassel&dq=ernest+hemingway+and+%22Tassel%22&lr=&ie=ISO-8859-1&output=html&source=gbs_search_r&cad=1