Punctuating this fragment is difficult.  The natural reading is the one given here, Burnet's translation.

Kahn, however, was not pleased with that reading.  He punctuated as follows: "The limits of dawn and evening are the Bear;  and opposite the Bear [is] the guardian of bright Zeus."

Burnet's translation says that there are two limits: the Bear and the guardian of bright Zeus.
Kahn's translation says that there is one limit: the Bear.