28 VERTEBRATE ANIMALS OF THE UNITED STATES 



Key to the Divisions of Pisces 



ai Skeleton cartilaginous; skull without membrane bones; sharks; 



skates; (all marine, not included in this book) i. Selachii. 



0.2 Skeleton in most cases bony; skull with membrane bones. 



bi Paired fins each with a segmented cartilaginous axis; respiration 

 by gills and lungs (no American species and hence not 



included in this book) 2. Dipnoi. 



hi Fins supported by fin-rays and without central axes 3. Teleostomi. 



Division 3. Teleostomi.^ — Skeleton usually bony; skull covered 

 with membrane bones separated by sutures; a single gill opening on each 



Fig. 13. — Buccal funnel of Lampetra lamoUejtii {from Creaser b' Hohbs). 



side, the gills being supported by 4 pairs of arches in most cases, and 

 covered by the opercles; air bladder mostly present: 2 series. 



Key to the Series of Teleostomi 



ai Skeleton cartilaginous or bony i. Ganoidea. 



3,2 "Skeleton bony 2. Teleostei. 



Series i. Ganoidea. — The ganoid fishes. Fishes with either car- 

 tilaginous or bony skeleton; with heterocercal or homocercal caudal fin; 

 with either ganoid or cycloid scales or bony dermal plates; with an air 



