274 



MINERALS AND GEOLOGY 



circular. Usually smooth, or marked simply by concentric '. 

 growth. 



This family, of the highest antiquity, still offers living representa- 

 tives. The principal genera comprise Lingida, Lingulella, and 

 Obolus. The shell in linyula is without a foramen, the pedicel, as 

 seen in living species, passing out between the valves. Tn lingulella 

 and in obolus, there is a narrow marginal foramen in one valve. 

 These genera date from the Cambrian period. In the strata of 

 Ontario and Quebec, examples of lingulae are of frequent occurrence. 

 Usually the shell is dark and lustrous ; but in examples from the 

 Medina formation of Hamilton, Ontario, it preserves its normal sub- 

 pearly and iridescent aspect. Some of our more characteristic species 

 are shewn in the annexed figures. 



207. 



203. 204. 205. 206. zu '- 207 bin. 



Fig. 203. Lingula acuminata (= L. antiqua) Potsdam (Cambrian) 

 formation. 



Fig. 204. L. Quebecensis : Levis formation. 



Fig. 205. L. Lyelli : Chazy formation. 



Fig. 206. L. quadrata : Trenton formation. 



Fig. 207. L. obtusa : Utica and Hudson River formations. 



Fig. 207 bi. L. oblonga (Conrad) : Medina and Clinton forma- 

 tions.* 



* This small species of lingula is abundant in some of the red, Medina strata of Hamilton, 

 Ontario. In many examples the substance of the shell is preserved. 



