Let it be borne in mind that Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, Orbicula, Lingula, Rhynchonclla, and Nautilus, all of which are existing genera, are given without a doubt as Silurian in the last edition of "Siluria"; while the highest forms of the highest Cephalopods are represented in the Lias by a genus Belemnoteuthis, which presents the closest relation to the existing Loligo.