34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



lary to frontal such that the line of contact between these 

 bones extends backward in a neari} horizontal direction 

 over the entire orbit, leaving no broad area of the frontal 

 exposed over middle of orbit when skull is viewed from the 

 side]. 

 Maxillary with a freely projecting plate-like process ex- 

 tending backward toward squamosal ; pterygoid with- 

 out reduplication either external or internal IniidtE. 



Maxillary with no backward-extending plate-like process ; 

 pterygoid with reduplication, either external or internal 

 or both. 



Pterygoid greatly enlarged [covering alisphenoid], the 

 area of its outer side equal to that of base of brain- 

 case [its reduplications low and ridge-like] ; teeth 

 of adult reduced to one or two in lower jaw, absent 

 in upper jaw; rostrum deepened and solidified; 

 hindermost ribs supported by transverse processes 

 which appear to be not serially homologous with 



those which support the others Ziphiid.e. 



Pterj'goid not enlarged, the area of its outer side less 

 than that of base of braincase ; teeth of adult not 

 reduced to one or two in lower jaw, normally 

 present in upper jaw; rostrum not deepened and 

 solidified; hindermost ribs (except possibly in some 

 extinct genera) supported by transverse processes 

 which appear to be serially homologous with those 



which support the others Delphinid.e. 



Alisphenoid not overspread by pterygoid ; internal 

 reduplication of pterygoid present, usually well 

 developed ; no external reduplication. 



Teeth not tusk-like in manner of growth ; 

 dentition never reduced to a single for- 

 ward-projecting tusk. 



Intermaxillary never extending conspicu- 

 ously forward beyond maxillary. 



Dclphinlncs. 

 Intermaxillary said to extend conspicu- 

 ously forward beyond maxillary. 



Eurhinoddphininw. 

 Teeth tusk-like in manner of growth ; denti- 

 tion reduced to a single forward projecting 

 tusk, usually present in one maxilla of male 



only Monodontincc. 



Alisphenoid overspread by pterygoid ; both in- 

 ternal and external reduplications of pterygoid 

 normally present. 



Pterygoid with reduplications large ; teeth of 



normal delphinine type Stenodclphinincs. 



Pterygoid with reduplications small ; teeth 

 tusk-like in manner of growth. Dclphiiiapfcrina. 



