black and yellow snake in my yard.

[Skiploder]

t. s. sirtalis "florida blue" have some of the best looking "enlarged rear teeth" (i don't type it this way because the phrase rather annoys me, I have always been taught "rear fangs") I have seen on a garter.

Some species of garters have nominally enlarged rear fangs. That does not make them opistoglyphs like hydrodynastes, rhamphiophis, boiga, etc.

An opistoglyph not only has enlarged rear fangs, but delivers venom via a grooved channel in them. It is an evolutionary delivery step above having rear fangs and no channel.

The word glyph means carved or grooved channel............an aglyph lacks that channel.

So while a boiga, for example, has grooves in those enlarged rear teeth to make the venom delivery more effective, thamnophis does not.