David Wilson
Contributor
I remember as a kid having a mask with built in snorkels with the ping pong balls in the cage.
Here's a snorkel mask that still appears to be in production at the Greek diving equipment manufacturer Majorca Sub:
http://www.majorcasub.gr/products/03-004.jpg
Just one attached snorkel, though.
To view historical examples of snorkel masks, some with twin snorkels, see illustrations 18-26 in the Italian Historical Diving Society document below:
http://www.hdsitalia.com/articoli/20_attrezzature.pdf