484 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Peachella iddingsi — Continued. page 



compared with Callavia broggeri 344 



Olenellus ? argentus 315 



Olcnellus canadensis 343 



Olenellus frcnwnti 343 



JVanneria gracilc 343 



mentioned 248, 285 



stratigraphic distribution tabulated 251 



Peak, A. C, bibliographic reference 218 



pealei, see Micromitra. 



Pedicle, defined 157 



Pedicle furrow, defined 157 



Pedicle groove, defined 158 



Pedicle muscles, defined 158 



Pedicle opening, defined 158 



Pedicle tube, defined 158 



Pelias, see Obolus mcconnelli. 



Pentameracea, classification of 142 



defined 148 



microscopic shell structure of Cambrian and Ordovician compared. 153 



spondylium in 159 



perfectus, see Obolus (Fordinia) . 



Perkins, Prof. George H., acknowledgments 235 



perseus, see Conocephalus. 

 pcrugata, see Kntorghia. 



Phtlhedra, classification of 142-147 



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



Philhedra columbiaua, stratigraphic position and association 210 



Pioche, fossils from 86, '87, 285, 322, 329, 345 



Pioche formation, correlated with the Mount Whyte formation 12 



defined 1 1 



fossils from 322, 329, 345 



House Range, correlated 171 



section of 184, pi. 17 



Nevada, fossils in 86, 87 



piochensis, see Ptychoparia. 

 pisiformis, see Agnostus. 



Platform, defined 158 



Platyceras bellianus, stratigraphic position and association 210 



primcEVtim, mentioned 341 



romingeri, stratigraphic position and association 210 



sp. undt., stratigraphic position and association 181, 183, 199, 213 



Plectorthis, compared with Eoorthis 104 



strictly defined by Hall and Clarke 103 



Grabau and Shimer, in synonymy 102 



Hall and Clarke, in synonymy 102 



see Orthis {Plectorthis). 



Plectorthis plicatella, thin section of 164, pi. 12, fig. 8 



Pleurocoeles, defined 158 



