I have several types of Bucephalandra and if there is anything that I have learned is that currently the naming system is anything but well defined. Its seems most are just variants of a few species, but that may well prove wrong when taxonomists get round to properly identifying them all. There are a few distinct varieties... you can't easily get a dark Achilles wrong, but many are visually only slightly different from other types. Your plant has a nice look and form, but I could not say what it is with certainty. Can you ask the people who sent it or was it a long time ago?