Mekhilta of Rabbi Shimon bar Yochai is falsely believed to be implied in the title Sifre de-Bei Rav in contradistinction to R. Shimon b. Yochai's midrash.
It is clear, therefore, that the Mekhilta of R. Shimon was implied in the title Sifre de-Bei Rav; and it is mentioned in the Midrash Tehillim under the Hebrew name Middot R. Shimon b. Yohai. 
