The genomes of myonecrotic Clostridium perfringens isolates contain genes encoding a large and fascinating array of highly modular glycoside hydrolase enzymes. Though the catalytic activities of many of these enzymes are somewhat predictable based on their amino acid sequences the functions of their abundant ancillary modules are not and these remain poorly studied. Here we present the structural and functional analysis of a new family of ancillary carbohydrate-binding module (CBM), CBM51, which was previously annotated in databases as the NPCBM domain. The high resolution crystal structures of two CBM51 examples, GH95CBM51 and GH98CBM51, from a putative family 95 -fucosidase and from a family 98 blood group A/B-antigen specific endo--galactosidase, respectively, showed them to have highly similar -sandwich folds. However, GH95CBM51 was shown by glycan microarray screening, isothermal titration calorimetry, and X-ray crystallography to bind galactose residues while the same analysis of GH98CBM51 revealed specificity for the blood group A/B-antigens through non-conserved interactions. Overall, this work identifies a new family of CBMs with many members having apparent specificity for eukaryotic glycans, in keeping with the glycan rich environment C. perfringens would experience in its host. However, a wider bioinformatic analysis of this CBM family also indicated a large number of members in non-pathogenic environmental bacteria suggesting a role in the recognition of environmental glycans.