There are 3 titles associated with this firm.

@book{ wphp_18530
  author={Montagu,Elizabeth},
  year={1810},
  title={The Letters of Mrs. Elizabeth Montagu, With Some of the Letters of her Correspondents. Published by Matthew Montagu, Esq. M.P. her Nephew and Executor.},
  publisher={William M'llhenny},
  address={Boston},    }
@book{ wphp_15392
  author={Montagu,Elizabeth},
  year={1810},
  title={The Letters of Mrs. Elizabeth Montagu, with Some of the Letters of Her Correspondents. Published by Matthew Montagu, Esq. M.P. her nephew and executor. In three volumes.},
  publisher={William M'llhenny},
  address={Boston},    }
@book{ wphp_19105
  author={Porter,Jane},
  year={1810},
  title={The Scottish chiefs, a romance. In three volumes. By Miss Jane Porter, author of Thaddeus of Warsaw, and Remarks on Sidney's aphorisms.},
  publisher={Bradford and Inskeep \& Inskeep and Bradford \& William M'llhenny \& Edward Johnson Coale \& Morford, Willington, & Co.},
  address={Philadelphia},    }