PEIMARY SUBDIVISIONS OF THE CETACEANS. 123 



forwards laterally above the temporal fossae. 

 Frontals visible above only as elongated hook- 

 shaped borders produced backwards around the 

 maxillaries. 



a. Costal cartilages not ossified. The tuber- 

 cular and capitular articulations of the ribs 

 blending together posteriorly. (Flower.) 

 Lachrymal bones coalesced with the Ju- 

 gals. Orbit very small. PLATANISTID^. (in.) 



h. Costal cartilages firmly ossified. Posterior 

 ribs losing their capitular articulation, and 

 only uniting with the transverse processes 

 of the vertebrae by the tubercle. (Flower.) 

 Orbits moderate. DELPHINID^. (IV.) 



c. Costal cartilages not ossified. The hinder 

 ribs losing their tubercular, and retaining 

 their capitular articulation with the verte- 

 brae. (Flower.) Lachrymal bones distinct 

 from the Jugals. ziPHim^. (V.) 



II. Upper jaw not rostrated or marginated ; snout high 

 towards the front and projecting beyond the 

 mouth. Skull raised behind and retrorsely con- 

 vex. Supraoccipital projecting forwards laterally 

 above the temporal foss£e. Frontals visible above 

 as erect triangular or retrorsely falciform wedge 

 between the maxillaries and supraoccipital. 



PHYSETERID^. (VI.) 



B. Rostrum of skull prolonged into a slender, straight 

 beak, the premaxillary and maxillary bones forming 

 a cylinder, bearing teeth on its proximal portion. 



RHABDOSTEID^. (VU.) 



III. PLATANISTID^ Flower. 

 Subfamilies. 



1. Maxillary bones with crests null or little developed. 

 Many of the teeth with a complete cingulum, or a 

 distinct tubercle at the base of the crown. 

 a. Postorbital and zygomatic processes discon- 

 nected. Jugal with a well developed, curved, 

 ante-orbital process. Maxillary not contract- 

 ed, without crest, and with convex free mar- 

 gin at suborbital region. IwxSM. 



