480 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



PAGE 



Olenus asaphoides Fitch, in synonymy 269 



Olenus (Olenellus) gilberti Gilbert, in synonymy 324 



Olenus {Olenellus) hozuelli Gilbert, in synonymy 324 



Onaqui Range, Utah, fossils in 68 



onaquiensis, see Obolus (Westonia) ella. 



Ophileta, stratigraphic position and association 204 



ophirensis, see Acrotreta and Mieromitra (Iphidella) pannula. 

 ophirensis descendens, see Acrotreta. 



Opisthoparia, defined 235 



trilobites belonging to the order described 18-41 



Orbiculoidea, classification of 142, 147 



evolution of pi. 11 (pp. 140-141) 



Ordovician Protremata compared with Cambrian articulates 151-153 



Ordovician rocks, sections of j 173, 191, 204 



ornatella, see Mieromitra {Iphidella'). 

 ornatus, see Bathyuriscus. 



Orr formation, correlated 171 



defined 10 



fossils in 91, 92 



section of I75-I77, pl. 15, fig. i 



Orthacea, classification of 142 



defined 147 



Orthidas, chemical composition of shells compared with that of Billings- 



ellidae 152 



Orthis, compared with Eoorthis 104 



evolution of pl. 11 (pp. 140-141) 



strictly defined by Hall and Clarke 102-103 



Orthis (or Orthisina) sp., Etheridge, in synonymy 109 



Orthis cequivalvis (Hall) , mentioned 103 



callactis Dalman, mentioned 102 



calligramma, mentioned 103 



ftssicosta Hall, mentioned 103 



jamesi Hall, mentioned 103 



plicatella, mentioned 103 



remnicha Winchell, mentioned 103, 104 



sinuata, mentioned 103 



suhquadrata, mentioned 103 



tricenaria 102 



triplicatella Meek, mentioned 103 



Orthis {Dalnianella) parva. mentioned 104 



Orthis {Plectorthis) Walcott, in synonymy 102 



Orthoceras, stratigraphic position and association 191 



Orthotheca adamsi, mentioned 300 



corrugata, stratigraphic position and association 210 



major, stratigraphic position and association 197, 210 



sp. undt, stratigraphic position and association 185, 199 



Orusia, classification of 142, 148 



evolution of pl. 11 (pp. 140- 141) 



