- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Several specimens of Metriophyllum gracile collected from a locality in the type area (middle Devonian) in the Eifel region, Germany, show a distinct groove extending from the apical end about one-third the length of the corallum. It is suggested that the groove formed with the growth of the coral as a result of being anchored to a stem such as a seaweed which decomposed leaving no trace. Specimens from other localities in the same area and at the same horizon show either a bulbous expansion or a rootlike process for attachment. Also noted is a change in form from trochoid to nearly cylindrical where the corallum attains maximum diameter, and a shift from the longitudinal ridges at the apical end to more prominent growth striations at the distal end, with a constriction at the junction. No change in relative rate of growth could be detected, but there seems to have been a pause at the point of maturity.