T-Rex Dinosaur Birthday Party Invitations (20 Count with Envelopes) Includes 20 Invitations and 20 Envelopes Heavy Weight Cardstock. 4 x 6 Inches. Flat Two Sided Design with Full Color on Front and Back. Fill in the Blank details: For, Date, Time, Place, RSVP. Cute Prehistoric Dino Kids Birthday Invites with T-Rex, Brontosaurus, and Stegosaurus dinosaurs.