112 A POPULAR EXPOSITION OF THE 



naria; j5^. 92, 0. pectinella, and fig. 93, O. lynx, all of common 

 occurrence in the Trenton Grroup. O. elegantula of the Niagara 

 Group (Upper Silurian) is closely related to O. tesfudinaria, and has 

 the general form of fig. 90. 0. Vanuxemi, fig. 94, is a Devonian 

 species. The Lower Silurian form, O. lynx, fig. 93, has the general 

 aspect of a spirifer, but its mesial fold and sinus are marked by 

 several plications, a character not exhibited by any of our Canadian 

 Spirifers. It was formerly called Delthyris lynx. 



StropJiomena : — Shell, concavo-convex ; hinge-line, straight ; no 

 internal supports. This genus ranges from the Silurian to the 

 Carboniferous formation. Canadian examples are very abundant. 



Fig. 95. ^''^^^■ 



Fig. 95 represents S. alternata, a species of exceedingly common 

 occurrence in the Trenton and Hudson Eiver Groups (Lo.wer 

 Silurian.) S.fiUtexta is a closely related form. Pig. 96 exhibits 

 another well-known species, S. rhomhoidalis {= StropJiomena and 

 Leptana depressa,) from the Niagara Group and other Upper 

 Silurian strata, and also from the Devonian rocks of Western Canada. 

 In ^these latter rocks a few species of Ghonetes and Productm, 

 (genera allied to StropJiomena,) also occur. 



Zepteena .—This genus (or rather sub-genus,) merely differs from 

 StropJiomena by the character and elongation of 

 its muscular impressions. L. sericea, Eig. 97, 

 of the Trenton and Hudson Eiver Groups, is a 

 species of common occurrence. yx^. 97. 



Spirifer : — Shell with internal calcareous processes in the form of 

 two spiral coils pointing outwards. Hinge-line straight, long ; area 

 well developed, with triangular foramen. The genus ranges from 

 the Silurian to the Triassic (or Jurassic) epoch, but is chiefly charac- 

 teristic of Upper Silurian, Devonian, and Carboniferous rocks. Pig. 

 98 represents S. Magarensis of the Upper Silurian, and Fig. 99, S, 



