The cells are chlorophyllous, fewer in number, dumb-bell in shape and inner walls are thick. This description fits to

Each stoma is composed of two bean-shaped cells known as guard cells which enclose stomatal pore. In grasses, the guard cells are dumb-bell shaped. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata.