Frying donuts split along the sides So, I rolled out some lovely old-fashioned donuts and cut them out... got my oil to 340... and proceeded to fry them. Instead of lovely “blistering” at the top of the donut, mine seemed to split along the sides... looking like 2 halves of a donut held together in the middle.

What could have caused this? This is my first foray at frying donuts.
I'd guess your doughnut dough was too dry.

I've seen doughnuts with a pale ring around the sides, I'd guess it came from either less contact with oil (if floating fairly high) or from the sides stretching as the heat made the dough puff up, which meant less direct oil contact for the newly stretched dough surface.  

For dough to split instead of stretch while cooking, I'd look to similar reasons this happens, eg, in bread - which can include being dry (and especially the surface drying to form a skin, which doesn't stretch), not rising enough beforehand so the "oven spring" is overenthusiastic - which might be a cause for yeast doughnuts though not other varieties, and so on.

With the information that those who tried the doughnuts found them "dry" and "crunchy", I'd go with my first guess of there not being enough moisture, so the dough wasn't flexible enough.  If they sat out long enough to form a dried skin, this would be especially likely to cause splitting.  Moister dough, or keeping covered better, or brushing with water, etc just before frying, might all work to ameliorate this problem.