Take away CBS's Under the Dome and ABC's two first-run dramas, Mistresses and Motive, and all the major networks would be down below last year in the summer's Nielsen ratings, Broadcast & Cable observed on Tuesday. Fox, it noted, is struggling the most with an average of just 3.1 million viewers versus 4 million last summer. The exception: the two Spanish-language channels, Univision and Telemundo. In fact Univision was the highest-rated network in July among the 18-49 age group. Telemundo scored as the fastest-growing network in that age group, up 30 percent. It was also up 22 percent among total adults.