152 BULLETIN 36, UNITED STATES NATIONAL MUSEUM. 



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



pterygoid bones not esteudiug backward across the optic canal to articnlate with 

 the s(iuamosal. 

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

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



of the superior nares convex 14. Grampus. 



Maxillary and mandibular teeth both present. 

 Teeth with compressed, spade-shaped crowns. 



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



Rostrum exceeding one-third the total length ot the skull , 12. Phocwim. 



Teeth conical, rugose. 

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



in contact - 2. Stow. 



Teeth conical, smooth. 



Palate with two distinct lateral grooves 4. Delphinus. 



Palate without lateral grooves. 

 Rostral portion of iutermaxilljB convex. 



Pterygoid bones separate 1. SotaJia. 



Pterygoid bones in contact. 



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



Teeth larger (22 to 26) 3. Tursiops. 



Rostral portion of iutermaxillio 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 jilane of the 

 surrounding surfaces. 

 Maxillie not thickened about the maxillary notch. 

 Outer border of the proximal end of the intermaxillse overhanging the 



adjacent surface of the maxilhe 6. Tursio. 



Outer border of the proximal end of the intermaxiilte continuous with 



the adjacent border of the maxilla; 10. Cepbalorhyndnis. 



Maxilhe thickened about the maxillary notches. 



Teeth small and numerous 7. Lagenorhijnclius. 



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

 rostrum. Pterygoid bones in contact. 

 IntormaxilhB greatly expanded on the rostrum, covering the greater 

 part of the maxilhe. Teeth confined to the anterior half of the 



rostrum 15. Globicephahis. 



IntermaxillsB 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. 



Intermaxilhe of equal breadth throughout . 16. Pseudorca. 



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 maxilhe in the same 

 plane with the distal portion. 

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



18. Delphinaplerns. 



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 I'J. Monodon. 



