56 THE VOYAGE OF H.M.S. CHALLENGER. 



edge of the maxillary root of the zygoma, from which spot the palate diminishes in 

 transverse diameter both forwards and backwards ; posterior border either truncated or 

 emarginate. Articulation of vomer with floor of the nose variable in position. Carotid 

 canal distinct from and antero-external to the foramen lacerum posterius. Occipital 

 condyles converging anteriorly, their articular surfaces frequently continuous ; basi- 

 occipital flattened and usually perforated mesially. Anterior nares far from terminal. 

 Malar variable in its length. Neck short. Hind limbs directed backwards, not used in land 

 locomotion. Front limbs smaller than posterior, digits armed with strong terminal claws. 



1-1 . 5-5 



Palms and soles hairy. Dentition — incisors variable, canines f3j. post-canines g— g. 



Mammas 2 or 4. Scapula with prse- and postspinous fossss almost equal in area. 

 Humerus with or without supra-condyloid foramen. Ilium with crest much everted and 

 in transverse plane of base of sacrum. Femur with small trochanter absent or rudi- 

 mentary. Astragalus with a long calcanear process. 



Trichechid^e. 



Without pinna of ear and scrotum ; postorbital processes either wanting or rudi- 

 mentary ; alisphenoid canal large ; mastoid massive but not entirely discontinuous from 

 the tympanic bulla ; posterior border of nasal articulating with anterior border of frontal 

 almost in the transverse plane of skull. Inner wall of orbit complete, but that of 

 zygomatic fossa defective. Lateral borders of hard palate almost parallel to each 

 other behind, though somewhat converging anteriorly ; posterior border truncated. 

 Vomer articulating with floor of nose well in front of hinder border of palate. Carotid 

 canal distinct from and in front of foramen lacerum posterius. Basi-occipital mesially 

 keeled and not perforated. Anterior nares terminal. Malar short. Neck longer than 

 in Phocidse. Palms and soles hairless ; manus and pes can be turned forwards and used 

 for land locomotion. Upper canines 1-1, elongated into great tusks. Mammas 4. 

 Scapula with prsespinous much larger than postspinous fossa. Humerus without a 

 supra-condyloid foramen. Ilium with crest everted and in front of base of sacrum. 

 Femur with rudimentary small trochanter. Astragalus without a calcanear process. 



Otariid^e. 



With pinna of ear and scrotum ; postorbital processes distinct ; alisphenoid canal 

 present ; mastoid quite discontinuous from tympanic bulla and prominent ; tympanic 

 bullae only slightly swollen ; anterior mesial process of frontal passing between the 

 diverging posterior ends of the nasals. Inner wall of the orbit very defective, so that 



