CETACEA. 311 



cervical vertebrae ankylosed together ; no functional teeth in 

 the upper jaw; pectoral limbs small; dorsal fin usually 

 present. 



c. Teeth in lower jaw, 20 to 25 in number; rostrum greatly 

 elongated ; mandible long and narrow, the symphysis 

 occupying more than half the length of the ramus. 



Physeter, p. 314. 



c^. Teeth in the lower jaw, q to 1 2 in number ; rostrum short, 

 not exceeding the cranium in length; mandibular 

 symphysis less than half the length of the ramus. 



Kogia, p. 315. 



b^. Costal cartilages not ossified ; the tubercular and capitular 

 articulation of the ribs blending posteriorly; cervical verte- 

 brae all free ; mandibular symphysis very long, exceeding 

 half the length of the ramus ; dorsal fin rudimentary ; eye 

 rudimentary; fluviatile or estuarine. Platanista, p. 315. 



b^. Costal cartilages firmly ossified ; posterior ribs lose their capi- 

 tular articulation and are united to the transverse processes 

 of the vertebrae by the tubercular process ; some of the ante- 

 rior cervical vertebrae generally ankylosed ; numerous teeth 

 in both jaws; symphysis of mandible short or moderate, not 

 exceeding \ of the ramus ; dorsal fin usually present, 



[= Delphinidae.] 



d. With rounded head ; no distinct rostrum or beak ; in the 

 skull the rostral equals the cranial portion in length ; 

 atlas and axis firmly united ; pterygoids small and 

 widely separated. 



e. Crowns of the teeth laterally compressed ; teeth |f to 

 f§; no dorsal fin. Neomeris, p. 318. 



e^. Crowns of the teeth conical and pointed. 



/, Pterygoid bones widely separated from one another; 

 teeth H to fl small, occupying the whole length 

 of the rostrum. Orcella, p. 318. 



/2. Pterygoid bones normal, meeting in the middle 



line ; teeth |- to y\ occupying only the anterior 



part of the rostrum; dorsal fin low and triangular. 



Giobicephalus, p. 319- 



/3. Pterygoid bones normal, meeting in the middle 

 line ; teeth small ff to ||, not exceeding 4 mm. 

 in diameter; rostrum slightly exceeding in length 

 the cranium. 



Lagenorhynchus, p. 21. 



