Police believe an armed man who has robbed multiple convenience stores north of Boston has struck again — this time in Reading. The suspect entered a gas station convenience store at 85 Main St. in Reading at 10:45 p.m. Thursday and showed the clerk a black handgun, Reading police said in a statement. The robber took several hundred dollars from the cash register, police said. He is described as a white male, 6 feet tall, 180 pounds, wearing black pants, a black sweatshirt, and a mask, police said.