CAMBRIAN GEOLOGY AND PALEONTOLOGY 

 III 



No. 3.— CAMBRIAN TRILOBITES 



By CHARLES D. WALCOTT 



(With Plates 24 to 38) 



CONTENTS 



PAGE 



Introduction 160 



Change in stratigraphic position 161 



Descriptions of genera and species 161 



Order Proparia Beecher 161 



Family Menomonidae, new family 161 



Menomonia, new genus 161 



Menomonia calymenoides (Whitfield) (pi. 26, figs. 4, ^a-d) . . 162 



Millardia, new genus 163 



Millardia avitas, new species (pi. 28, figs. 5, 5a-c) 165 



Millardia optata (Hall) (pi. 28, figs. 4, 4a-/) 165 



Millardia seniele, new species (pi. 28, figs. 3, 3a-c) 166 



Drcsbachia, new genus 166 



Drcsbachia adnata, new species (pi. 26, figs. 5, 5a-c) 167 



Norwoodidae, new family 168 



Norwoodia, new genus 168 



Norwoodia gracilis, new species (pi. 27, figs. 2, 2a-g) 169 



Norwoodia ponderosa, new species (pi. 28, figs, i, la-b) 171 



Norwoodia saffordi, new species (pi. 27, figs, i, la-f) 171 



Norwoodia simplex, new species (pi. 27, figs. 3, 3a-b) 171 



Norwoodia tenera, new species (pi. 28, figs. 2, 2a-g) 172 



Order Opisthoparia Beecher 1 73 



Genus Agraulos Corda " 173 



Agraulos stator, new species (pi. 36, fig. 6) 173 



Genus Acrocephalites Waller ius 174 



Acrocephalites americanus, new species (pi. 24, figs. 2, 2a-b , 



2, Za-b) 177 



Acrocephalites aoris, new species (pi. 26, figs. 3, ^a-b) 178 



Acrocephalites ? aster, new species (pi. 26, figs. 9, ga-c) 178 



Acrocephalites ? glomeratus, new species (pi. 26, figs. 7, ya) . . 179 



Acrocephalites haynesi, new species (pi. 24, figs. 4, 40-&) 179 



Acrocephalites insignis, new species (pi. 25, figs, i, la-b) .... 179 



Acrocephalites ? majus, new species (pi. 26, fig. i) 180 



Acrocephalites multisegmcntus, new species (pi. 24, figs. 5, 5a) 180 



Smithsonian Miscellaneous Collections, Vol. 64, No. 3 



157 



