_Josephiana_, of the natural size, Trenton
Limestone, Canada; j, The same, viewed from the front. (After
Salter, M'Coy, Rupert Jones, and Dana.)]
The Ringed Worms (_Annelides_) are abundantly represented in the
Lower Silurian, but principally by tracks and burrows similar
in essential respects to those which occur so commonly in the
Cambrian formation, and calling for no special comment. Much more
important are the _Articulate_ animals, represented as heretofore,
wholly by the remains of the aquatic group of the _Crustaceans_.
Amongst these are numerous little bivalved forms--such as species
of _Primitia_ (fig. 47, f), _Beyrichia_ (fig. 47, e), and
_Leperditia_ (fig. 47, i and j). Most of these are very small,
varying from the size of a pin's head up to that of a hemp seed;
but they are sometimes as large as a small bean (fig. 47, i),
and they are commonly found in myriads together in the rock. As
before said, they belong to the same great group as the living
Water-fleas (_Ostracoda_). Besides these, we find the pod-shaped
head-shields of the shrimp-like Phyllopods--such as _Caryocaris_
(fig. 47, d) and _Ceratiocaris_. More important, however, than
any of these are the _Trilobites_, which may be considered as
attaining their maximum development in the Lower Silurian. The
huge _Paradoxides_ of the Cambrian have now disappeared, and with
them almost all the principal and characteristic "primordial"
genera, save _Olenus_ and _Agnostus_.
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