Both the gun on the pic are Lewis gun
This will help you to distinguish between the various Lewis guns:
from top to bottom":
A. Lewis 1914 "infantry" pattern (without butt, replaced by handles), also called Lewis MkI
(Russian aircraft often used regular infantry Lewis with the wooden butt)
E. Lewis "stripped" "infantry" pattern, also called "Lewis aircraft MkI",
G. "Lewis aircraft MkII",
K. "Lewis aircraft MkIII"
L. "Lewis RNAS pattern" (a "super stripped" MkI)

Here are the various forms of expanded cartridge pouches on a Lewis Aircraft MkI ("stripped infantry" pattern):

And here are the Vickers used in WW1 (Confusion comes from the fact that Post ww1 Vickers indeed look superficially like Lewis aircraft guns):
A. Vickers MkI "infantry pattern"
B. Vickers MkI "aircraft pattern 1916"
C. Vickers MkII "aircraft pattern 1917" (almost not used in ww1, but the standard aircraft weapon of the interwar years)
