Some of this same
tribe of shells, such as Camarophoria, allied to Rhynchonella, Spiriferina, and
two species of Lingula, are specifically the same as fossils of the
carboniferous rocks. Avicula, Arca, and Schizodus (Figure 410), and other
lamellibranchiate bivalves, are abundant, but spiral univalves are very rare.
(FIGURE 417. Restored outline of a fish of the genus Palaeoniscus, Agassiz.
Palaeothrissum, Blainville.)
Beneath the limestone lies a formation termed the marl-stone, which consists of
hard calcareous shales, marl-slate, and thin-bedded limestones. At East
Thickley, in Durham, where it is thirty feet thick, this slate has yielded many
fine specimens of fossil fish-- of the genera Palaeoniscus ten species,
Pygopterus two species, Coelacanthus two species, and Platysomus two species,
which as genera are common to the older Carboniferous formation, but the Permian
species are peculiar, and, for the most part, identical with those found in the
marl-slate or copper-slate of Thuringia.
(FIGURE 418. Shark. Heterocercal.)
(FIGURE 419. Shad. (Clupea. Herring tribe.
Pages:
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720