That's a pcv-valve. It should be connected to intake below carb. And on the other valve cover should be a filtered connection for replacement air.
Do a search on PCV and you'll probabaly get more detailed information.
-Sami
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.