CAMBRIAN GEOLOGY AND PALEONTOLOGY 



II 



No. 3.— MIDDLE CAMBRIAN HOLOTHURIANS AND 



MEDUSA 



By CHARLES D. WALCOTT 



(With Six Plates) 



CONTENTS 



PAGE 



Introduction 42 



Holothurians 43 



Class Holothurioidea 45 



Family Eldoniidee, new family 45 



Genus Eldonia, new genus 45 



Eldonia hidzvigi, new species 46 



Muscles 46 



Radial canals 47 



Alimentary canal 48 



Genital organs 49 



Family Holothuriidae 52 



Genus Laggania, new genus 52 



Laggania cambria, new species 52 



Genus Loiiisella, new genus 53 



Louisella pedunciilata, new species , 53 



Family Synaptidse 53 



Genus Mackenzia, new genus 54 



Mackensia costalis, new species 55 



Scyphomedusse 55 



Order Rhizostomas 55 



Family Undetermined 55 



Genus Peytoia, new genus 55 



Pcytoia nathorsti, new species 56 



Burgess shale. New name proposed in footnote 51 



PLATES 



Plate 8. Peytoia nathorsti and Eldonia ludzvigi 58 



9. Eldonia lud-wigi 60 



10. Eldonia ludwigi 62 



11. Eldonia ludzvigi 64 



12. Eldonia ludzvigi d^ 



13. Laggania cambria, Mackensia costalis, and Louisella prdun- 



culata 68 



Smithsonian Miscellaneous Collections, Vol. 57, No. 3 



41 



