Samples collected from the Dundee Limestone at St. Mary's, Ontario yielded 3400 identifiable conodont specimens representing 16 genera and 33 species. Three "groups" of conodont species are recognized, based on their distribution in the section. Group I (Angulodus walrathi, Hindeodella austinensis, Neoprioniodus pronus, Ozarkodina congesta, Icriodus nodosus, Panderodus sp., and Acodina formosa) is distributed generally throughout the section. Group II (Plectospathodus sp., Polygnathus linguiformis linguiformis and Ozarkodina lata) occurs from near the base of the section to the 24-ft (7-m) level and from the 28- to 39-ft (8.5- to 12-m) levels. Group III (Ligonodina delicata, Lonchodina arcuata, Neoprioniodus alatus, Neoprioniodus n. sp., Polygnathus robusticostata and Prioniodina aversa) occurs only from the 24- to 3 3-ft (7- to 10-m) levels. The presence and absence of conodont "groups" can be related to changes in lithology of the limestone.The distribution of the "groups" of conodonts and their apparent relation to lithological changes suggest the following: 1. Group II may consist of shallow, quiet water conodonts; 2. Group III may consist of conodont species which existed in a shallow water environment with good water circulation; and 3. the conodont animal was probably nektonic during some stage in its life cycle rather than planktonic, and possibly benthonic during another stage.