206 A POPULAR EXPOSITION OF THE 
_. Fig. 205.—Ambonychia Fig. 206.—Modiolopsis modiolaris (Conrad). Fiz. 207.~Oyr- 
radiata (Hall,) tolites orna- 
tus (Conrad) 
Fig. 208.—Orthoceras crebriseptum Fig. 209.—COalymene Blu- 
(Hall). menbachtt (Brogniart). 
In addition to the above, the following species (figured under the 
Trenton Group, ona preceding page) are also of common occur- 
rence :—Stenopora fibrosa (fig. 177); Petraia cornicula (fig. 178) ; 
Orthis testudinaria (fig. 182); Strophomena alternata (fig. 186) ; 
Rhynconella increbescens (fig. 187) ; Orthoceras bilineatwm (fig. 193) ; 
O. lateralis (fig. 192) ; Drinucleus coneentricus (fig. 195); Asaphus 
platycephalus (fig. 196); and Illenus crassicauda (fig. 196 a). 
In western Canada, the Hudson River formation occurs as an 
outlier in the vicinity of Ottawa City, associated with the bitumi- 
nous shales of the Utica series. Its chief development in this sec- 
tion of the Province, however, is between the more western extrem- 
ity of Lake Ontario, and the Western shores of Georgian Bay. It. 
forms the shore-line of Lake Ontario from the River Rouge in the 
Township of Pickering (Ontario Co.), to the River Credit in Toronto 
