Joann:
The part of the wheel that begins at the inside of the
tire and extends inward until the next concentric circle is
the "split ring" or "split rim". The split appears as a
wavy squiggly the bottom of this ring; that is where the
ring is split so it can be expanded outward slightly and
removed by lifting it off the wheel. Split ring wheels
require tubes be used inside tires to hold air in tire
because otherwise the air would leak out of the split in the
ring and from around the inside of the ring where it meets
the wheel. Those joints are not air tight.
Good eye on the valve. As you noticed, the valve hole can
also sometimes identify a split ring wheel. Sometimes the
hole for the valve to come through is oblong. That hole
doesn't have to be air tight because the air is inside the
tube and cannot leak through the oblong hole in the wheel.
One piece wheels usually have round valve stems (typically
rubber nowadays) that fit through a hole and become air
tight upon inflating the tire.