3DS + Vita according to NPD leaks sold approximately 175k in February 2014. Which indicates that 3DS is down year over year again (it sold 183k last Feb). Assuming Vita sold it's usual pathetic 20k or so, that would put the 3DS at 155k guesstimate.
Compartively at this point in last gen, (Feb 2008) DS was selling 588k and the PSP at 243k. That means even the second place PSP is selling way more at the same point in its life than the 3DS + Vita *combined*. That means the handheld business is only about 20% of what it was last gen.
Lets go back even further to the GBA generation, the GBA alone was selling 353k for Feb 2004. So it's lagging behind the GBA gen too.
This can't really be a content issue either, the 3DS has had a great library of releases with Bravely Default selling well in Feb and Pokemon X/Y out and also the new cheaper 2DS model this year.
