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Show 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-phorina, 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 l.-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 somewhat 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 structure 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 of 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 transversely. 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 1 Eosmarus, Gesner, Hist. An. Aquat. (1558) p. 249. Odobcenus, Linn. Syst. Nat. i. (1735) p. 59. Trichechus Linn. Syst. Nat. i. (1766) p. 49 ; De Blainville, Osteog.: Cuv. Oss. Foss Atlas, ii. pi. 219 bis; Schreber's Fortgesetzt Wagner, vii. p. 77 ; Murie, Trans Zool' Soc. vii. (1871) p. 411, pis. 51-55; Gray, Cat. Seals Brit. Mus. (1866) p. 35, and P. Z. S. (1853) pp. 112-116; Allen, N. A. Pinnipeds, pp. 5-186. |