Z CHARACTERS OF PINNIPEDIA. 



consiilerable vacuities between the palatine aud frontal bones 

 and the tympanic and exoccipital bones. ' The deciduous den- 

 tition is rudimentary, never to any great extent functional, and 

 frequently does not jiersist beyond the foetal life of the animal. 

 In the permanent dentition, the canines are greatly developed, 

 sometimes enormously so; the lower incisors are never more 

 than four in number, and sometimes only two ; the upi)er incisors 

 usually niunber six, but sometimes only four, or even two ; the 

 grinding teeth (premolars and molars) are generally simple in 

 structure, and usualty differ from each other merely in respect 

 to size, or the number of roots by which they are insertetl. The 

 pelvis differs from that of the terrestrial Ferce in the shortness 

 of the iliac portion and the eversion of its anterior border ; the 

 ischiac bones barely meet for a short distance in the male, and 

 are usually widely separated in the female, the pelvic arch thus 

 remaining in the latter permanently open ventrally. 



The existing Pinnipeds constitute three very distinct minor 

 groups or families, differing quite widely from each other in 

 imjiortant characters : these are the Walruses, or Odohccnidw, the 

 Eared Seals, or Otariidce, and the Earless Seals, or Phocidce. The 

 first two are far more nearly allied than are either of these with 

 the third, so that the Odohwnidce and Otariidw may be together 

 contrasted with the Phocidce. The last named is the lowest or 

 most generalized group, while the others appear to stand on 

 nearly the same plane, and about equally remote from the PJio- 

 cidm. The Walruses are really little more than thick, clumsy, 

 obese forms of the Otarian tyi)e, with the canines enormously 

 developed, and the whole skull correlatively modified. The 

 limb-structure, the mode of life, and the whole economy are 

 essentially the same in the two groups, and, aside from the cran- 

 ial modifications presented by the OdohcvnidcVj which are obvi- 

 ously related to the develoinnent of the canines as huge tusks, 

 the Walruses are merely elephantine Otariids, the absence or 

 presence of an external ear being in reality a feature of minor 

 importance. 



The characters of the suborder and its three families may be 

 more formally stated as follows : * 



*Tlie characters Iiere given are in part those collated hj' Dr. Theodore K. 

 Gill in 1873 ("Arrangement of the Families of the Mammals."' Smithsonian 

 Miscellaneons Collections, Ko. 230, pp. 56, 68, 69), by whom the distinctive 

 features of these groups ^vere first formulated. They have, however, been 

 carefully verified and fiu-ther elaborated by the present writer, while the 

 families are here quite differently associated. 



