When I first saw this clam shell at a fair a while back I was not thinking Victorian. I thought maybe an unknown maker and possibly somewhat later.
On close inspection both pieces are marked with the Davidson lion trade mark. The colour looks more like the purple slag glass that they did in the mid 1960's , but then it would not have been marked. So 1880-90 is most likely the date it comes from.
Measures 5" in length and 2" in height.