Fig. 74.—Belemnite.—After Philips.
Fig. 74a.—Belemnoteuthis antiquus. Supposed to be a Belemnite, with soft parts preserved.—Jurassic.—After Mantell.
I have reserved no space to notice the geological history of the other and higher group of Cephalopods, including the true Cuttles and Squids. This is perhaps less to be regretted, as, from the absence of external shells, they are likely to be much less perfectly known as fossils. So far as known, they are vastly younger than the Nautiloids, for no examples whatever have been found in the Palæozoic. They appear abundantly in the Mesozoic, but are there represented principally by an extinct group of squids (Belemnites and their allies, [Figs. 74, 74a]), remarkable for the great and complicated development of their internal support, which has a chambered float as well as a solid sheath. This family becomes extinct at the close of the Mesozoic, though the cuttles as a whole perhaps culminate in the modern.
Fig. 75.—Cambrian Trilobites.