LOS ANGELES – Amid an emerging rivalry between traditional pay TV operators and rising star Netflix Inc., CBS Corp.’s Showtime pay TV service confirmed Wednesday that back seasons of current original series like “Dexter” and “Californication” will not be available on Netflix’s streaming service as of this summer.

Instead, CBS will offer them to subscribers who pay for Showtime through Comcast Corp. on Comcast’s Xfinity TV platform.

The deal has been in place since February, but news of the details broke this week after Netflix announced it was buying the right to debut the series “House of Cards” from executive producer David Fincher.

Debuting an original series on its service makes Netflix even more of a direct rival to pay TV channels like Showtime and HBO. Netflix had 20.2 million subscribers in the U.S. at the end of December, compared with 20 million for Showtime and HBO’s estimated 28 million.

Showtime originals that have stopped airing on TV, including “The Tudors” and “Sleeper Cell,” will continue to be available for streaming on Netflix.

CBS and Netflix announced a two-year deal last month that allows older shows that are not generating new original episodes to be run on Netflix’s streaming service, including “Medium,” “Frasier” and “Cheers.”

The deal followed a 10-year pact that CBS cut with Comcast in August that allowed for CBS and Showtime shows to be played on Comcast’s Xfinity TV platform, which can be accessed on computers and iPad tablets.

CBS is seeking to maximize the money it can receive from Netflix from older content, while encouraging consumers to pay separately for new original shows on Showtime.

Goldman Sachs analyst Ingrid Chung said the impact of CBS pulling some shows from Netflix would not materially affect Netflix, but it could signal that it will have to pay more for the right to stream shows in the future.

CBS shares closed up 21 cents Wednesday at $24.87. Netflix shares finished the regular session up $7.67, at $229.06.