It's difficult to tell the difference within a section such as between alcohol inkys C. Atramentaria and C. Striata (slightly pointier).

But the C. Lagopus group is pretty different, they're less than half the size, they're covered in white hairs when they're young, and they have flesh so thin that it turns inside out and transparent as the inside starts to turn to ink like you can see in OPs photo.

Compare to this photo from Wikipedia which shows how C. Atramentaria looks when it's turning to ink (or deliquescing if you're fancy).