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Kristen,
I would like to know answer myself.
I understood cf as:
There is, for example fly Xxx yyy, then one discovers that it is realy group of related species - Xxx yyy, X. yyy1, X. yyy2. In this case one of this group mya be labeled as cf Xxx yyy.
But according Diptera.info Glossary "cf" = "?"
Nikita