Have any of you ever seen a floor drain that doesn't have a trap in it?

In our house half the basement is finished and the other half unfinished, both have floor drains in lowest part of the room. The one in the unfinished part always worked, albeit slowly, but recently stopped and when snaked by a plumber he came across mud and some small roots after about four feet.

I only discovered the other drain in the finished half when pulling up the floor; the lineoleum tile was glued in place right over it. This drain worked but I noticed a very small bit of odor from it and also could feel air moving in it.

Both drains appear to be about 8" vertical to a stop, then a 90 degree pipe coming in that carries the water off. Normally the bottom of the drain is dry.

Question: in the 1930s was it common to put in a floor drain without a trap or could there be a trap further along in the drain, under the floor? Am I right to think these are not hooked to the sanitary sewer because of the lack of smell and the air moving through them?