Memoirs of the Geological Survey of the United Kingdom

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. It would appear from these facts that the ventral edge of the aperture of the phragmocone is parallel to the sutures of the septa, and that, on the sides, it curves round almost at a right angle to form an elongated lobe, which terminates in an ogive arch on the dorsal side.