rectangular, black with a white stripe up the legs. Lightweight too. I love 'em, and they only cost me £20! yay NHS!
As a side note, I thought my eye's were pretty bad at -2.5D considering most people I know hover round -1 to -2. However, I read in an interview that Claudia Winkleman (British TV presenter)had a prescription of -14. Now I don't feel so bad!