CONTENTS 



Side-Gilled Saw-Fishes (Pristiophorus) — True Saw-Fishes (Pristis)— Beaked Rays 

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

 (Raiidce) — Electric Rays (Torpedinidai) — The Eagle-Rays (Myliobatidw) — Typical Genus 

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

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

 (Acanthodii), . . . ... 



520 



THE LOWEST VERTEBRATES AND THEIR 



ALLIES 



CHAPTER I. — The Lamprey Group, — Class Cyclostomatb. 



Characters of Chordates and Non-Chordates — Lampreys and Hag-Fishes (Subclass 

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

 — Hag-Fishes (Myxinidce) — Primeval Lampreys (Palceospondylus), . . . 549 



CHAPTER II. — The Armoubed Primeval Vertebrates, — Subclass Ostracophori. 

 Pteraspis — Cephalaspis — Pterichthys, ........ 555 



CHAPTER III. — The Lancelets, — Subkingdom Protochordata — Class Leptocardii. 

 Common Lancelets (Branchiostoma), ........ 558 



CHAPTER IV. —The Sea-Squirts or Ascidians, — Class Tunicata. 



Structure of Ascidians — Development — Typical Ascidians — Non-Luminous Pelagic Ascidians 



— Tailed Ascidians, . ...... 561 



CHAPTER V. — Worm-Like Protochordates, — Class Enteropneusta. 

 Balanoglossus — Other Forms — Ancestry of Chordates, ...... 573 



Index ............ 577 



