The galactan of the snail Helix pomatia was subjected to two cycles of Smith-degradation and the resulting products were isolated by gel filtration and thin layer chromatography. 2. The structures of the low molecular weight oligosaccharides were elucidated being identical to those obtained from Lymnaea stagnalis galactan. However, the quantities released differed significantly between the two species. The high molecular fractions comprising about 66% of the material were not obtained in a similar degradation of the Lymnaea stagnalis galactan. 4. Thus the observed structural differences can explain easily the species-specific reactivity among the two polysaccharides seen earlier with lectins, enzymes and antibodies.