122 



HISTORICAL PALEONTOLOGY. 



also very common examples of the Tabulate corals during this 

 period, though they occur likewise in the Lower Silurian. 



Amongst the Echinodermata, all those orders which have 

 hard parts capable of ready preservation are more or less 





d 



Fig. 59. a, Haly sites catenularia, small variety, of the natural size ; 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 ; rf, Vertical section of two tubes 

 of the same, showing the tabulae, 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 (Echinoids) are said 

 to be represented by examples of the old genus Palcechinus. 

 The Star-fishes (Asteroids} and the Brittle-stars (Ophiuroids) 

 are, comparatively speaking, largely represented, the former 

 by species of Palasterina (fig. 60), Palaaster (fig. 60), Palazo- 

 coma (fig. 60), Petraster, Gly piaster, and Lepidaster and the 

 latter by species of Protaster (fig. 61), Palaodiscus, Acroura, 

 and Eucladia. 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 



