The Arduino Uno SMD uses the same microcontroller but in a QFP package. In both cases pin 24 on the microcontroller connects to A1 (which is also D15 or simply pin 15). Note that as long as you are just using the provided Arduino library functions and declarations you never need to know what the package pin or the GPIO port of the microcontroller is being referenced. So just forget "24". 
On your folllowup post where you say 68 zeroes then a valid value, which repeats, is there one second between each zero value? The pulseIn function with only two arguments will timeout and return a zero after one second without seeing input. If it is returning a zero faster I would guess it is seen very short pulses that it cannot measure. And in that case you really need an oscilloscope to see what is going on. You would be having some signal integrity issue from the receiver.