They seem to be a c1910 - 1930s phenomenon. I did a trawl through the Sick Collection slides once upon a time looking for them.

If anyone spots one from somewhere else, let us know...

LATER, after a search, found this interesting sample card from birdi, showing variations of 7-point murrine clear into the 1990s, evidently:

http://beadcollector.net/cgi-bin/anyboard.cgi?fvp=/openforum/&cmd=iYz&aK=88424&iZz=88424&gV=0&kQz=&aO=1&iWz=0