SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 57 



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Ottoia proUfica, stratigraphic position and association 153 



ovalis, see Hynienocaris. 



Paleozoic ages, referred to 166 



Paleozoic Crustacea 164-165 



Paleozoic formations, mentioned 155 



parva, see Hynienocaris. 

 perfecta, see Hynienocaris. 



Peytoia nathorsti, stratigraphic position and association 153 



Phyllocarida, descendant from Branchiopoda 164 



first known in Lower Cambrian by Isoxys 155 



foreshadowed by Burgess shale fauna 165 



represented by Nebalia 162 



mentioned 162 



Phyllopod bed, described and subdivided 152 



PJiysa, ancestors of 166 



Pikaia gracilens, stratigrahpic position and association 152 



Plate descriptions 208-228 



platycephalus, see Asaphus. 

 platyurus, see Thamnocephalus. 

 plena, see Yohoia. 

 pleurexanthemns, see Ceraurus. 



Pleurons, triangular-shaped, in Yohoia tenuis 172 



Pollingeria grandis, stratigraphic position and association 153 



Polyartemidse, remarkable adaptation of 165 



Pre-Cambrian, marine sedimentation 161 



Merostomata represented in 155 



Proboscis of Opabiiiia rcgalis 169 



Protocaris, single specimen of 157 



Protopodite, thoracic appendage 159 



Pterogotus bilobus, compared with Sidneyia inexpectans 206 



Ptychoparia, appendages of 190 



Ptychoparia cordillerce (Rominger), appendages of 190, 192 



Rami, caudal 158, I59 



furcal 166 



regalis, see Opabinia. 

 retifera, see Tuzoia. 



Scenella varians, stratigraphic position and association 153 



Section of phyllopod bed 152 



Sedimentation, pre-Cambrian marine 161 



Segmentation, table of cephalic, thoracic, and abdominal segments 158 



Selkirkia gracilis, stratigraphic position and association 153 



Selkirkia major, stratigraphic position and association 153 



senaria, see Calyniene. 



Sericite 151 



serratus, see Neolenus. 



Sessile eyes, Burgessia and Marrella i59 



