1889.] Synopsis of the Families of Vertebrata. 857 
Ventral fins usually thoracic or jugular; no ductus 
pneumaticus ; usually a spinous dorsal fin; parie- 
tal bones usually separated by the supraoccipital ; 
scales usually ctenoid ; Physoclysti. 
PHYSOSTOMI. 
I. Median fin rays with actinotrichia. 
Intercentra distinct, small ; no centra. '^Lysopteri. 
II. Median fin rays equal to and articulating with axonosts. 
«, Vertebrae complex, the pleurocentra and intercentra 
distinct. 
Anterior vertebrae similar ; Merospondyli. 
aa, Vertebrae with centra and intercentra both complete 
on part of the column at least; amphiccelous; 
Anterior vertebrae similar; H aleconw^phi. 
«««, Vertebrae (intercentra) opisthoccelous. 
Anterior vertebrae similar; a precoracoid arch and 
a coronoid bone; Ginglymodi. 
a«««, Vertebras (intercentra) amphicoelous. 
/5 J, Precoracoid arch. 
y^ No symplectic bone. 
Pterotic simple ; anterior vertebrae modified, and 
with ossicula auditus ; parietals not distinct ; Neniatognathi- 
Pterotic annular, including a cavity which is closed 
by a distinct bone; anterior vertebrae simple, 
without ossicula auditus; parietals distinct ; Scyphophori. 
rr,-^ symplectic bone. 
Anterior vertebrae coossified and with ossicula 
auditus ; pterotic simple ; Plectospondyli. 
Anterior vertebrae not modified ; pterotic simple ; 
parietals distinct ; Isospondyli. 
/5/}, No precoracoid arch. 
y^ Scapular arch suspended to cranium. 
•5, A symplectic. 
Anterior vertebrae and pterotic simple ; parietals 
separated by supraoccipital ; Haplomi. 
Anterior vertebrae modified ; parietals not separated ; Glanencheli. 
