Please help me identify a part

Hello,

I'm in the process of putting everything back together after replacing the head gasket on my '12 Prius Four but can't find the black piece that is near his hand in this screen shot. Can someone help identify it for me so I can order it?

I think it's the thermostat housing gasket, but it's raining and I don't want to go looking at the car and parts in the rain.

Thanks!

 

Perhaps I should specify, the black circular piece near his right hand on the timing cover is not on mine and I'm not absolutely positive what it is.