Different identifying marks in Harpa species?

[sakura-of-the-sea]

I was wanting to know if there are any different ID markings between <i>H. major</i>, <i>H. davidis</i> and <i>H. articularis</i>. I have looked through countless field guides & without written descrïptions, I can't distinguish between them. Only the listed names give away the species.
What should I look for in case I receive an unknown <i>Harpa</i> that looks most like either of these three species? <img src="images/smiley/confused.gif" alt="" border="0" />