Niagara Limestone (Wenlock), Canada. (Original.)]
[Illustration: Fig. 60.--Upper Silurian Star-fishes. 1, _Palasterina
primoeva_, Lower Ludlow; 2, _Paloeaster Ruthveni_, Lower Ludlow;
3, _Paloeocoma Colvini_, Lower Ludlow. (After Salter.)]
[Illustration: Fig. 61.--A, _Protaster Sedgwickii_, showing the
disc and bases of the arms; B, Portion of an arm, greatly enlarged.
Lower Ludlow. (After Salter.)]
Amongst the _Echinodermata_, all those orders which have hard parts
capable of ready preservation are more or less largely represented.
We have no trace of the Holothurians or Sea-cucumbers; but this
is not surprising, as the record of the past is throughout almost
silent as to the former existence of these soft-bodied creatures,
the scattered plates and spicules in their skin offering a very
uncertain chance of preservation in the fossil condition. The
Sea-urchins (_Echinoids_) are said to be represented by examples
of the old genus _Paloechinus_. The Star-fishes (_Asteroids_) and
the Brittle-stars (_Ophiuroids_) are, comparatively speaking,
largely represented; the former by species of _Palasterina_ (fig.
60), _Paloeaster_ (fig. 60), _Paloeocoma_ (fig. 60), _Petraster,
Glyptaster_, and _Lepidaster_--and the latter by species of
_Protaster_ (fig. 61), _Paloeodiscus, Acroura_, and _Eucladia_.
The singular _Cystideans_, or "Globe Crinoids," with their globular
or ovate, tesselated bodies (fig.
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