COLUMBIA, Md., Jan. 31 -- Corvis Corp., a maker of switching and routing equipment for fiber optic networks, has agreed to acquire privately held Dorsal Networks for about $90 million in stock. The acquisition of the undersea optical network equipment provider will expand the market for Corvis, which has focused on selling land-based equipment, the company said. Corvis will acquire Dorsal for about 40 million shares, and the deal is expected to be completed in the second quarter.