Essentially identical versions of this classifications are presented in Oswalt and McLendon's "Introduction" to the Pomo chapters in Heizer, ed. (1978) and in Campbell (1997). The most important dissenter was Abraham M. Halpern, one of the few linguists since Barrett's time to collect comparative data on all of the Pomoan languages. Halpern's classification differed from Oswalt's mainly in the placement of Northeastern Pomo. Instead of considering it an independent branch of the family, Halpern grouped it with the languages of Oswalt's "Western" branch, suggesting the possibility that Northeastern Pomo represents a recent migration of a Northern Pomo subgroup (Halpern 1964; Golla 2011:106-7).