This site http://www.houseofnames.com/xq/asp.fc/qx/lowndes-family-crest.htm perports to give you an accurate family history, but for Lowndes at least there are many errors and I do not recommend it.
The Arms are incorrect (and frankly odd). The description suggests that the family came to England with the Norman Conquest, but then states that the name Lowndes has an Old English derivation! Such a basic mistake is worth a giggle, but little else.
I’ve yet to find one of these companies that cares enough to get it right (or as right as we can get). I recommend anyone after a ‘crest’ creates one from the freely available images on my site, or employs a professional Heraldic expert.