PRIMARY SUBDIVISIONS OF THE CETACEANS. 123 



forwards laterally above the temporal fossae. 

 Frontals visible above only as elongated hook- 

 shaped borders producer! 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^B. (in.) 



b. 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. DELPHlNnxas. (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. ziPHinxs;. (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 fossae. Frontals visible above 

 as erect triangular or retrorsely falciform wedge 

 between the maxillaries and supraoccipital. 



PHYSETERID^E. (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^;. (VII.) 



in. PLATANISTIDuE 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. 



