Diagnosis.- Cicatricula whose individual canals range from 0.08 to 0.32 mm in diameter, most falling in the range of 0.12-0.20 mm. The canals are sinuous, and branch at least every millimetre. The whole boring may reach a size of 14 mm across, and is circular or oval in plan.

Discussion. - The individual canals of Cicatricula retiformis are too large to be of fungal or algal origin. A sponge is more likely to have been responsible. The widened, rounded corners of the bifurcations and intersections are reminiscent of CIiona borings.This characteristic is not typical of boring bryozoans or phoronids, which furthermore normally produce long straight, or gently curving tubules (see Pohowsky 1974; Voigt 1975).