If lawn and turf experts say it's a slime mold, then it probably is, but it sounds like you asked here after asking them? I'm interested to learn there are slime molds that can grow in grass, I didn't know that until you posted this, and thought they needed a mulched bed to show up.
This guy has a pic of something similar he's calling slime mold:
http://www.alansblog.org.uk/?p... (about halfway down the page)
And this gal had something interesting in her yard:
http://peonyden.blogspot.com/2...
No combo of search words I tried involving 'slime mold' brought up pics that looked the same as what you've pictured though. A fairly funky fungus ;+) I'll be watching this!
