Not stated. Clearly a diminutive relating to William McIntosh (who had used the homonym Langerhansia replaced here ... [details]
feminine. -ella is the feminine form of the diminutive -ellus -a -um [details]
Replacement name for Langerhansia McIntosh, 1885; originally as Polynoe (Langerhansia) McIntosh, 1885: 108-109 [details]