Bought as Fenton. Could be Fenton, Tiffin or Diamond. This one has an opening of 6 1/2"; Height of 3 1/8"; Foot 2 7/8" by 1/8".
Madeley and Shetlar's "American Iridescent Stretch Glass Identification & Value Guide" show a bowl which most people think is more like this shape than others found in that book under their section on Diamond Glassware (plate 9). Unfortunately forum members with Diamond bowls think that their bowls are much thicker glass than the bowl shown.
This bowl has a much smaller base in proportion to the rim than what is usually associated with Tiffin. The color certainly looks like Tiffin though. Tiffin was researched extensively to try and find this shape but none was found.