The biometry of the Clyde population of long rough dabs has been studied and compared with the descriptions of the European race given by Norman in his monograph of the flat-fishes. The data consist of various body measurements together with the results of scale counts, fin ray counts and vertebral counts. The fin ray numbers fit into a pattern of increasing number with high latitudes when compared with other published data. There is a correlation between the number of anal and dorsal fin rays, and between these and the number of vertebrae. The variations that were found in the vertebrae of fifty-one fish are described. Only one sinistral long rough dab has been found out of 2357 specimens examined. From the British fishing statistics it is shown that the long rough dab is of little, and declining, commercial importance. In Canada, however, the American subspecies is becoming more important commercially.