Epiphylliums(sp?) cacti

[nash at mudshark.sunquest.com]

By default, I have ammassed a large collection of tropical forest cactus. For 
the most part (amateur that I am) I have them correctly identified, especially 
those in the rhipsalis group. However, over the years people have given me 
starts of different epiphyllium cacti which I haven't been able to key out.At 
the moment my front porch is ablaze is vermillion, screaming yellow, pink, and 
white blooms coming from the old wood on these plants. 

My question: does anyone out there in netland know of a good sourcebook that 
would help me identify these things so I could at least learn their 
correct taxonomic classifications and how to spell them? The big cactus book 
put out by the University of Arizona press isn't of much help and the "Exotica" 
compendiums that cost $280 only show a few black and white photos then noting 
that there are many differnt kinds. 

Any info of this family (as well as zygocatus) would be greatly appreciated.

Keep watering.