152 BULLETIN 36, UNITED STATES NATIONAL MUSEUM. 



2. ARTIFICIAL KEY TO THE GENKRA, BASED ON CRANIAL CHARACTERS. 



pterygoid boues not extending baciiward across the optic canal to articulate with 

 the sciuamosal. 

 Maxillary teeth decidnous, absent in adult skulls. Mandibular teeth few, con- 

 fined to the region of the symphysis. Triaugiilar area in front 



of the superior uares convex 14. Grampus. 



Maxillary and mandibular teeth both present. 

 Teeth with compressed, spade-shaped crowns. 



Rostrum one-third the total length of the skull 11. Neomcris. 



Rostrum exceeding one-third the total length of the skull , 12. I'hocwna. 



Teeth conical, rugose. 

 Mandibular symphysis long ; rostrum very long and narrow. Pterygoid bones 



in contact - 2. Sleno. 



Teeth conical, smooth. 



Palate with two distinct lateral grooves , 4. Dclphiiiits. 



Palate without lateral grooves. 

 Rostral portion of intermasilhe convex. 



Pterygoid bones separate 1. Sotalia. 



Pterygoid bones in contact. 



Teeth small and numerous (37 to 52) 5. Prodelphiniis. 



Teeth larger (22 to 26) 3. Tursiops. 



Rostral portion of iutermaxilho flat. 

 Triangular area in front of superior nares raised, forming a prominent 



table 8. Sagmatias. 



Triangular area in front of superior nares not raised above the plane of the 

 surrounding surfaces. 

 Maxilhc not thickened about the maxillary notch. 

 Outerborder of the proximal end of the intermaxilla} overhanging the 



adjacent surface of the maxilhe 6. Tursio. 



Outer border of the proximal end of the intermaxillte continuous with 



the adjacent border of the maxilhie 10. Cephalorhijnchus. 



Maxilla- thickened about the maxillary notches. 



Teeth small and numerous 7. Lagenorhi/nch us. 



Teeth few, confined to the anterior half or anterior two-tiiirds of the 

 rostrum. Pterygoid bones in contact, 

 luterniaxilliie greatly expanded on the rostrum, covering the greater 

 part of the maxilL'B. Teeth confined to the anterior half of the 



rostrum 1.5. Glohicephahts. 



Intermaxilhe moderate. Teeth in the anterior two-thirds of the 



rostrum 9. Feresa. 



Teeth few, small, occupying nearly the whole length of the ros- 

 trum. Pterygoid bones widely separated 13. Orcella. 



Teeth few and large ; roots cylindrical. Pterygoid bones in contact. 



Iutermaxilho of equal breadth throughout . 16. Pseiidorca. 



Teeth few and large with compressed roots. Pterygoid bones approx- 

 imated but not touching. Intermaxilhe expanded proximally. 



17. Orca. 

 Pterygoid bones extending backward across the optic canal and articulating with the 

 squamosal. Expanded proximal end of the maxilke in the same 

 plane with the distal portion. 

 Teeth present, irregular, obliquely implanted in the jaws. No tusks. 



18. Delphinapterus. 



Teeth only in the form of two straight tusks, concealed in the female. The left 



(occasionally the right also) greatly developed in the male and 



spirally grooved V). Monodon. 



