heptagon pair. The interface between the unit cells of the (8,0) and (5,3) half tubes contains three heptagons, three pentagons, and two hexagons. Two different matching orientations are possible: one with the two hexagons adjacent, the other without. We choose to study the configuration in which the hexagons are separated from each other. The sequence of n-fold rings around the circumference is then 6-7-5-6-7-5-7-5. In the tight-binding p-electron approximation [8], the (8,0) tube has a 1.2 eV gap [1] and the (7,1) tube is a semimetal. Within tight binding, these tubes form an