Grahame, I guess yours is this.
If so, this is a wideangle converter, as Birna noted. It seems to come with the dedicated closeup attatchment. Bower is the brand name also used for Samyang lenses. "0.42x" should mean that this converter shortens the focal length of the master lens by 0.42 times. 37mm is the diameter of the filter thread of a master lens. It could be designed for a small video camera?