Aha, another one we're researching as part of work on a Manchester glass book. We're a lot less sure on this one. We have density tested them all and this dog comes out at the highest value. There is some question as to whether any of these were originally candy containers with a card flap on the bottom, or what is the date range. My current thinking - subject to change - is this probably dates from about 1910-1940. If it is a Manchester maker, Burtles Tate would be the best guess - they made various things in black glass and at higher densities.
However it's a puzzler and I wouldn't want to put forward any attribution with confidence at the moment, would be interested in other opinions on this one.