@ Joe It's def slime mold, and here is a good read on it,

Slime Mold: Starving a Saprophytic Fungus

Peter Rennie, RPF
Consulting Forester and Arborist and contributor to my site, handled
this question on slime mold. Peter began by stating that slime mold is
not, technically, a lawn disease, but rather a saprophytic fungus (i.e.,
it is an organism that lives on dead organic matter).

So the most
logical way to get rid of slime mold is to cut off its food supply of
dead organic matter. What dead organic matter resides on your lawn?
Well, you certainly should be raking up leaves and twigs that have fallen on your lawn. But one of the biggest culprits is more difficult to see: lawn thatch. De-thatching
your lawn can sometimes seem like just so much busy work: until
something like slime mold comes along. Then you begin to realize the
importance of de-thatching the lawn.

Other Ways to Get Rid of Slime Mold

Peter also recommends the following for getting rid of slime mold:

• "allow more sun onto the lawn" (see below)
• "reduce watering for a while to allow it to dry out" (see below)

As
for using fungicides to get rid of slime mold, Peter writes that
Mancozeb will control the problem, but that it is "not considered worth
the cost."

"So, first," continues Peter, "I would suggest getting a
steel grass rake and rake the lawn hard (good exercise, you won't need
to go to the gym). Or get a thatching blade for your lawnmower (looks
like a regular blade but has two wires aimed to the ground to break up
the thatch).

"If you have moisture problems (low spot), try topdressing with sand and then overseeding. If you have big shading trees, you may want to thin them a bit to allow more light and air movement."