I've had a look at the Sowerby Registrations, but am sure this isn't one of theirs, and as we know many factories have produced this 'blackberries and cream' marbled colour - perhaps from the States?
Just as personal comment, and could be very wrong, but I don't get the impression that the butterfly as a relief decorative feature on pressed glass was common in the period 1870 - 1910, but it does appear more often in the art deco period 1925 - 1940 on such things as trinket sets and individual ornamental ware................ which is contrary to what you might think, bearing in mind the Victorians were obsessed with collecting butterflies and lining the undersides of glass trays with hundreds of blue wings from Morpho species.
I've looked at the pressed section in S. & F. but no butterflies, neither can I see a single specimen in either Thompson or Slack. With this colour of marble glass being common in the latter part of the C19, it is easy to assume this one is from that period, but it's only an assumption for now.
I like the head - more like a baby's head, or that of an old man, rather than a butterfly............ they don't have mouths as such, and their eyes are large and on the side of the head.
