x CONTENTS 



Side-Gilled Saw-Fishes (Pristiophorus) True Saw-Fishes (Prises) Beaked Rays 

 (Rhinobatidce) Typical Genus (Rhinobatis) Bhynchobatis The True Rays, or Skates 

 (Raiidce) Electric Rays (Torpedinidce) The Eagle-Rays (Myliobatidce) Typical Genus 

 (Myliobatis) Other Genera (Aetobatis, etc.) Sting-Rays (Trygonidce) Lobe-Finned 

 Sharks (Ichthyotomi) Fold -Finned Sharks (Cladodontia) Spine -Finned Sharks 

 (Acanthodii), ...... . 



THE LOWEST VERTEBRATES AND THEIR 



ALLIES 



CHAPTER I. THE LAMPREY GROUP, Class Cyclostomatc,. 



CHARACTERS OP CHORDATES AND NON-CHORDATES Lampreys and Hag-Fishes (Subclass 

 Marsipobranchii) True Lampreys (Petromyzum) Southern Lampreys (Mordacia, etc.) 

 Hag-Fishes (Myxinidw) Primeval Lampreys (Palceospondyhis), 



CHAPTER II. THE ARMOURED PRIMEVAL VERTEBRATES, Subclass Ostracophori. 

 Pteraspis Cephalaspis Pterichthys, ........ 



CHAPTER III. THE LANCELETS, Subkingdom Protochordata Class Leptocardii. 

 Common Lancelets (Branchiostoma), . . . . . . 



CHAPTER IV. THE SEA-SQUIRTS OR ASCIDIANS, Class Tunicata. 



Structure of Ascidians Development Typical Ascidians Non- Luminous Pelagic Ascidians 

 Tailed Ascidians, . . ...... 



CHAPTER V. WORM-LIKE PROTOCHORDATES, Class Enteropneusta. 

 Balanoglossus Other Forms Ancestry of Chordates, ...... 



INDEX 





