CONTENTS. 



Plates 1-18, text figures 1-154. 



PAGE 



Introduction 5 



Literature on Triassic Ichthyosauria 7 



Historical review of literature - 9 



Geologic and geographic occurrence 12 



Europe 



Spitsbergen 



New Zealand 14 



America 14 



(ieneral skeletal structure of the Triassic ichthyosaurs 20 



Skull : 20 



Facial region 21 



Pronto-parietal region 23 



Orbital region 23 



Temporal region 24 



Quadrate and suspensorium 25 



Palatine region . 26 



Mandible , 26 



Dentition 27 



Vertebrae 29 



Vertebra] formula 29 



Form of centra : 30 



Neural arches 33 



Hypocentral elements 36 



Atlas and axis 37 



Caudal fin .., '. '. 39 



Ribs 47 



Abdominal rib plastron 54 



Limb-arches : : 54 



Pelvic arch 54 



Pectoral arch : 58 



Limbs .. 63 



Mixosaurus and Cymbospondylus 65 



Merriamia 71 



Toretocnemus 71 



Delphinosanrus and Shastasaurus 72 



Stage of evolution of Triassic ichthyosaurs 73 



Origin of Ichthyosauria 77 



Variation in the Ichthyosauria 79 



Classification of the Ichthyosauria : 



Systematic descriptions 90 



Mixosaurus ( ?) atavus group 90 



Vertebral column 90 



Limb and arch elements 94 



Jaws and dentition 94 



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