MINERALS AND GEOLOGY OF CANADA, 



HI 



not exceeding fifty ; whilst the fossil spcci^tj discovered up to the 

 present timCj amount to over thirteen or Jt'ourteen hundred. They 

 constitute moreover, at least ninety per cent, of the bivalve shells 

 met with in the lower fossiliferous rocks. 



The following are the more important genera of Canadian occur- 

 ence : Lingula, Orthis, Strophomena, Leptoena, Spirifer, Athyris, 

 Spirigera, Atrypa, Wiynconella, Pentarherus, and Strichlandia. 



Lingula : — Shell : horny, thin, oblong, and nearly equivalve. Black 

 and shining in our examples, and consisting largely (as first shewn by 

 Prof. Sterry Hunt), of phosphate of lime. No internal calcareous 

 appendages. This genus ranges from the Lower 

 Silurian epoch into the present or existing period- 

 Numerous species occur in our Silurian formations. 

 Zi. quadrata, Hg. 89, from the Trenton Limestone, 

 Utica Slate, and Hudson Eiver Group (Lower 

 Silurian,) may be cited as a common example. 



Orthis : — Shell calcareous. Bi-convex or plano-convex ; with 

 straight hinge-line, and punctate surface No internal supports, 

 properly so-called. This genus ranged throughout the Palaeozoic 

 age, but was most abundant during the Silurian and Devonian 

 periods. The species have usually a more or less circular outline, 

 with the surface of the shell marked by fine or course radiating lines. 



FiK. 90. 



Fig. n. 



Fig. 92. 



Fig. 98. 



Fig. 94. 



Canadian examples are exceedingly numerous ; more especially those 

 belonging to O. testudinaria, fig. 90, of the Trenton and higher 

 divisions of the Lower Silurian series. Pig. 91 represents O. trice- 



