It is a Praying Mantis egg case.  You can easily see it on this branch of Rosemary.  It is about 1 1/2 inches in diameter.  

 

I don't know if the mantids have emerged yet, but this egg case holds about 100 babies.  You can read all about Praying Mantises at https://en.wikipedia.org/wiki/Mantis?wprov=sfti1  and learn more than you can possibly remember.  

 

My favorite part of the article describes Praying Mantises as "ambush predators."  That paints a pretty picture!!

 

It reminds me of our cat, Gizmo.  He loves to ambush critters, including US!!!

 

HAPPY GARDENING!!!