This is an interesting 303 from the French brand Stylomine. This particular model is called the "Mastodonte" (literally "giant" or "monster") because of its huge proportions. I've put a picture of the 303 with two Waterman's, a 52 and a 56 for scale considerations... Stylomine are known for their innovative filling systems and great ink capacity. The first Stylomine 303 came out at the beginning of the 1930's. The Mastodonte was launched in 1933 and the one presented here, if I'm not mistaken, is an early version.