Getting specific functions that need to be tested with code coverage

I'm working on some new node.js modules / apps and I'm writing tests for the functions.

I'm looking into the code coverage for the first time. I just got istanbul & mocha up and running.

$ istanbul cover _mocha -- -R dot    

And it prints out this nice report.

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  225 passing (931ms)

=============================================================================
Writing coverage object [/endeavor/coverage/coverage.json]
Writing coverage reports at [/endeavor/coverage]
=============================================================================

=============================== Coverage summary ===============================
Statements   : 87.59% ( 120/137 )
Branches     : 87.5% ( 14/16 )
Functions    : 74% ( 37/50 )
Lines        : 87.5% ( 119/136 )
================================================================================

However I'm looking for specifics, like what functions aren't being tested or "aren't covered". Istanbul also creates some files within a coverage directory, one of which is a html file, with no more info then what I get in the terminal.

How do I get a report of functions that aren't being tested? Is there a way to get this information from Istanbul, or another module?