120 HISTORICAL PALAZZONTOLOGY. 
Amongst the £chinodermata, all those orders which have 
hard parts capable of ready preservation are more or less 
Shoovesceut Gegerecrvcong 
1 
Fig. 59.—a, Halysites catenularia, small variety, of the natural size ; 4, Fragment of 
a large variety of the same, of the natural size; c, Fragment of limestone with the tubes 
of Halysites agglomerata, of the natural size; d, Vertical section of two tubes of the 
same, showing the tabulz, enlarged. Niagara Limestone (Wenlock), Canada. (Original.) 
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 (Zchznoids) are said 
to be represented by examples of the old genus Padechinus. 
The Star-fishes (Asteroids) and the Brittle-stars (Ophiurozds) 
are, comparatively speaking, largely represented ; the former 
by species of Palasterina (fig. 60), Paleaster (fig. 60), Paleo- 
coma (fig. 60), Petraster, Glyptaster, and Lepidaster—and the 
latter by species of Protaster (fig. 61), Paleodiscus, Acroura, 
and Lucladia. The singular Cystideans, or ‘“‘ Globe Crinoids,” 
with their globular or ovate, tesselated bodies (fig. 46, A, C, D,), 
are also not uncommon in the Upper Silurian ; and if they do 
not become finally extinct here, they certainly survive the close 
of this period by but a very brief time. By far the most im- 
portant, however, of the Upper Silurian Echinoderms, are the 
Sea-liles or Crizoids. ‘The limestones of this period are often 
largely composed of the fragmentary columns and detached 
