Complex sentence: The Appalachian cottontail and "S. transitionalis", the New England cottontail, are not easily distinguished in the field, and are most easily identified geogra or west of the Hudson River are considered Appalachian cottontails, those found north and east are considered New England cottontails.
Split into simpler sentences: The Appalachian cottontail and "S. transitionalis", the New England cottontail, are not easily distinguished in the field, and are most easily identified geographically. Cottontails found south or west of the Hudson River are considered Appalachian cottontails, those found north and east are considered New England cottontails.