In 1938, a symbol shaped similarly to heng
⟨ꜧ⟩ was approved as the official IPA symbol for the voiced alveolar lateral fricative, replacing ⟨ɮ⟩. It was suggested at the same time, however, that a compromise shaped like something between the two may also be used at the author's discretion. It was this compromise version that was included in the 1949 Principles of the International Phonetic Association
and the subsequent IPA charts, until it was replaced again by ⟨ɮ⟩ at the 1989 Kiel Convention
Despite the Association's prescription, ⟨ɮ⟩ is nonetheless seen in literature from the 1960s to the 1980s.