1885.] DR. ST. G. MIVART ON THE PINNIPEDIA. 493 



The canines are large, and the outer upper incisors rather so. 

 The molars are small and simple in structure. 



These two genera last described form a third small group, Cysto- 

 phorince, distinguished from the preceding by the dilatable skin of 

 the facial region of the males, the simple or plaited molars, and by 

 the presence of but two incisors in the lower jaw. 



The three subfamilies themselves agree in having backwardly 

 extended hind limbs, hairy palms and soles, no external ear, no 

 scrotum, well-developed canines in each jaw, five molars on either 

 side of either jaw, no alisphenoid canal, no frontal postorbital process 

 or only a small rudiment of such a structure, and a mastoid, which 

 rarely shows itself very distinct and apart from the auditory bulla. 



Trichechus \ — The Walrus inhabits the northern parts of both 

 the Atlantic and Pacific oceans. As is well known, its hind feet 

 are not constantly turned backwards (as in Phoca and its allies) but 

 are turned forwards during progression on land, but there is still no 

 external ear and no scrotum. The eyes are rather small. The 

 manus has five very small nails, and its digits are of about equal 

 length, as are also the digits of the feet, except that the fifth is some- 

 what the longest. It and the first have flattened nails ; those of the 

 other digits are large, compressed, and pointed. Cutaneous lobes 

 project beyond the nails of the first and fifth digits. 



There are 14 dorsal, 6 lumbar, 4 sacral, and about 18 caudal 

 vertebrae. 



The humerus is much longer than the radius and but little shorter 

 than the tibia, thus so far differing greatly from the skeletal struc- 

 ture of Phoca. 



The general characters of the skull are so familiar to naturalists 

 that it would be waste of time and space to give them here. It 

 differs from that oi Phoca in having no defects of ossification in the 

 occipital or the vicinity of the pterygoid. The suborbital foramen 

 is large. The zygomatic postorbital process, which is large, is 

 formed exclusively by the malar. There is no frontal postorbital 

 process. The anterior nares are small, heart-shaped, and very far 

 forwards. They are entirely bounded by the premaxillae and nasals, 

 which join, but the former are widely separated from the frontals, 

 and the latter (nasals) are quadrate and separate. The palate is 

 long and wide, and is concave both antero-posteriorly and trans- 

 versely. It has a more or less concave hinder margin, and the 

 pterygoid develops distinct depending hamular processes. There is 

 an alisphenoid canal. 



The bulla is undivided and very little prominent. The meatus 

 auditorius externus is not much produced outwardly. There is no 

 paroccipital process, but a very large and dense mastoid process, with 



^ Eosmarus, Gesner, Hist. An. Aquat. C 15.58) p. 249. 



Odobtsmis, Linn. Syst. Nat. i. (1735) p. 59. 



Trichechus, Linn. Sy.st. Nat. i. (1766) p. 49 ; De Blainville, Osteog. : Cuv. Oss. 

 Foss., Atlas, ii. pi. 219 bis; Sclireber's Fortgesetzt Wagner, vii. p. 77; Murie, 

 Trans. Zool. Soc. vii. (1871) p. 41 1, pis. 51-55 ; Grav, Cat. Seals Brit. Mus 

 (1866) p. 35, and P. Z. S. (1853) pp. 112-116; Allen, N. A. Piuuipeds, 

 pp. 5-186. 



