Analysis of the distribution of conodonts in sample sets measured down discrete beds exposed in the depositionally steeply dipping marginal-slope facies of the Upper Devonian reef complex of the Canning Basin has been undertaken in order to test the Seddon and the Druce interpretations of conodont biofacies. Each of the 14 sample sets was taken at measured intervals down single beds. The maximum difference in elevation between top and bottom samples was 65 m, indicating the water depth of the bottom sample to have been in excess of 65 m. Analysis of conodont distribution in the 53 sample points of the 14 sample sets does not indicate any clear depth segregation of conodont species that would correspond to the biofacies recognized by Seddon and Druce.

Because of the early paucity of Silurian conodont studies, it is still necessary to establish a comprehensive zonation and provide the sound systematics requisite for zonation of the Silurian System in North America. Current research indicates that the broad outlines of North American zones will closely parallel those defined in the Carnic Alps by Otto Walliser in 1964. In detail, however, modification is required, and the problems of provincialism and migration indicate need for some geographically restricted zones. The oldest Silurian conodont zone recognized in the Midwest, northern Michigan, and Ontario is yet to be named. Above it the limits of the Icriodina irregularis Assemblage Zone have been established in the same area, but provincial differences between the northern and southern areas are recognized. The next overlying zones, the Neospathognathodus celloni and the Pterospathodus amorphog-nathoides-Spathognathodus ranuliformis Assemblage Zones, have been documented in the Midwest and in the Niagara Gorge area. Younger zones have not been established, but a number of guide fossils of Walliser's zones have been recognized. Kockelella has been found in the upper part of the Louisville Limestone and in the Mississinewa Shale Member (Wabash Formation) in Indiana; Spathognathodus sagitta is present in the Lockport Dolomite in the Niagara Gorge and the St. Clair Limestone in Arkansas; Polygnathoides siluricus and Kockelella variabilis are included in the diversified fauna of the Bain-bridge Formation in Missouri and in the Lafferty Limestone in Arkansas; P. siluricus is also present in the Brownsport Formation and Decatur Limestone in Tennessee; Spathognathodus snajdri is found in the Kokomo Limestone Member (Salina Formation) in Indiana and the top of the Lockport Dolomite in New York; Spathog-nathodus eosteinhornensis is present in the Stonehouse Formation in Nova Scotia; and Spathognathodus remscheidensis is reported from the Syracuse Formation and younger Silurian strata in New York and from the upper part of the Decatur Limestone in Tennessee.