272 



MINERALS AND GEOLOGY 



198. 



195. 



199. 200. 



Fig. 195. S. rhomboidalis ( = S. depressa) : Upper Silurian and 

 Devonian. 



.Fig. 198. 0. tricenaria : Trenton Formation. 



Fig. 199. O.vanuxemi: Devonian. 



Fig. 200. Platystrophia lynx, the Delthyris lynx, afterwards 

 Spirifer lynx, and Orthis lynx, of old publications : Trenton forma- 

 tion. The plications on the mesial fold and sinus serve as a distinc- 

 tive character. 



Family 6. Productidce : Shell concavo-convex, free or attached by 

 surface of larger valve. Area absent or very narrow. Hinge-teeth 

 often rudimentary. No internal arm- supports. 



This family is entirely extinct. Its chief representatives comprise : 

 Productus, with very convex ventral valve and spiny surface, a 

 characteristic Carboniferous genus, but occurring also in Devonian 

 and Pernian strata j and Chonetes, with flat, transversely elongated 

 shell, bearing spines along] the hinge-margin. The latter genus 

 ranges from Silurian into Carboniferous strata, but the family is 

 unrepresented in the rocks of Central Canada. 



Division II. Inarticulata or Tretenterata : Brachiopods with 

 hingeless shell. In living forms, the intestine terminates in an anal 

 opening on the right side of the body. There are no calcined arm- 

 supports. 



This Division comprises the following families: 1, Trimerellidce ; 

 2, Craniadce ; 3, Discinidce 4, Lingulidce. 



