Wow that is one snazzy chart you got there! It really clarifies the ranges of all the ocs ive been looking at! Usually tenor, soprano, alto and bass have a designated range associated with them.
Looking at that very handy chart im noticing a couple things... the C6 to C7 range is entirely above the treble clef which is VERY high in terms of musical instruments. Where as C5 to C6 falls in the upper treble clef and above it. And finally C4 to C5 starts at middle C which falls directly between the bass and treble clef and goes to the top half of the treble clef. As far as a naming scheme goes, an instrument is generally named based on where the majority of range lies. I suggest:
C6 - C7 = Soprano
C5 - C6 = Alto
C4 - C5 = Tenor
C3 - C4 = Bass
C2 - C3 = Dbl Bass?
I realize by this naming scheme we have no Bass or Dbl Bass on the chart, but rest assured there are ocarinas that fall into this category, you know those REAL big ones im talking about? There arent to many on the market but they will come eventually, especially if I have anything to do with it

!!
And some people might say well there isnt now, changing a system like this to accommodate lower ocarinas will mess up the existing system, and like any good programmer knowns you always have to plan for the future.
Heck while we are at it we could come up with a whole naming system! Like... take for example a hind bass C ocarina, its made of wood, has a range of B3 to D5 which is 11 notes total plus 6 sharps/flats. So by my chart it fall in the Tenor range. So a short form description of it could look something like
Hind Bass C (Tenor)[B3-D5]{Range: 11 + 6}
So just by taking a quick look you know its range on our scale, the note range, and how many notes it covers + how many sharps/flats.

any thoughts?