What are the currently catchable Pokemon in Pokemon Go?

In Pokemon Go, what are the ranges, in Pokedex numbers, of currently catchable Pokemon?

I've tried searching and checking Niantic's website but I can't seem to find a good source that has these details.

UPDATED: 27.10.2017 Niantic will not directly say. Serebii maintains a list of available Pokemon. As of writing the Pokemon available are:

Generation 1

• 001-150 (Bulbasaur - Mewtwo)

Generation 2

• 152-234 (Chikorita - Stantler)
• 236-242 (Tyrogue - Blissey)
• 246-249 (Tyranitar - Lugia)

Special Halloween event 2017

• 302 (Sableye)
• 353-356 (Shuppet - Dusclops)

Since the direct answer to this question will change over time as more pokemon become available, you should regularly check Serebii or one of the other several websites which have well maintained and updated lists.