Want an Olsen-designed t-shirt?  Forget the Row, you better sign up with StyleMint now.

WWD reports that Mary-Kate and Ashley Olsen are launching a new e-commerce site called StyleMint. The billionaire duo has partnered with BeachMint, a brand-building e-commerce company headed by Myspace co-founder Josh Berman, to create an invitation-only site that will mix commerce with social media — and will feature, among other things, videos starring the twins.

As for actual merchandise, StyleMint is kicking off with a line of t-shirts starting at $29.99, which will be partially designed by the Olsens.  The site will be based on a monthly opt-out model, à la a book- or wine-of-the-month club — you join, then automatically receive the merchandise that’s featured that month, unless you choose not to receive it.

Ashley Olsen told WWD: “Online commerce is the perfect medium for us to create a new brand that is as much about the clothing as it is about the customer experience.”  Which is very true, though it gave us pause — don’t the Olsens already have a huge number of brands?  (Not to mention the fact that they are a brand, and have been for well over twenty years now.)  It’s interesting that they would create an entirely new line to go with an experiential site rather than expand upon the e-commerce experience of Elizabeth and James, or the Row, or even Olsenboye — all great, established brands with plenty of e-commerce potential.

Nevertheless, while we might be confused about how StyleMint qualifies as the Olsen’s ‘first’ e-commerce venture (the Row has an online shopping component, Olsenboye has a designated portion of J.C. Penney’s site),  we’ve nonetheless already registered our email address for an invitation.  We’re willing to put our trust in the Olsens  — they are the moguls, after all.