How can I map bytes to a matrix of structures?

[teo]

Here is an example of what I am after:

struct DATA
{
  ubyte D1;
  ubyte D2;
  ubyte D3;
  ubyte D4;
}

void main()
{
  ubyte[16] a = [ 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x01, 
0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08 ];
  auto b = (cast(DATA*)a.ptr)[0 .. 4];
  auto c = (cast(DATA[]*)b.ptr)[0 .. 2][0 .. 2];
}

I need to have a DATA[2][2]. That code compiles but gives me a 
segmentation fault.