TEETH OF DIPHYODONTS. 337 



below, as answering to those teeth which manifest the sectorial 

 character in the terrestrial Carnivora. The coadaptation of the 

 crowns of the upper and lower teeth is completely alternate, the 

 lower tooth always passing into the interspace anterior to its 

 fellow in the upper jaw. 



In the genus Plioca proper (Calocephalus, Cuv.) typified by 

 the common seal (Ph. vitulina), the dental formula is 



. 3.3 m 1.1 4.4 1.1 



The Sterrincks with double-rooted molars (Pelagius, Steno- 

 rhynchus} have four incisors above as well as below, i. e. J- :f . 



In the Saw-tooth Sterrinck (Stenorhynchus serridens), the 

 three anterior molars on each side of both jaws are four-lobed, 

 there being one anterior and two posterior accessory lobes ; the 

 remaining posterior molars (true molars) are five-lobed, the 

 principal cusp having one small lobe in front, and three de- 

 veloped from its posterior margin ; the summits of the lobes are 

 obtuse, and the posterior ones are recurved like the principal 

 lobe. 



The allied sub-genus (Ontmatophoca) of Seals of the southern 

 hemisphere has six molar teeth on each side of the upper, and 

 five on each side of the lower jaw, with the principal lobe of the 

 crown more incurved. 



In the genus Otaria the dental formula is- 



.3.3 1.1 4.4 2.2 



Z - I C - \ p 1 Til ~ - = GO. 



22 1144 1.1 



The two middle incisors are small, sub-compressed, with the 

 crown transversely notched; the simple crowns of the four 

 incisors below fit into these notches ; the outer incisors above are 

 much larger, with a long-pointed conical crown, like a small 

 canine. The true canine is twice as large as the adjoining in- 

 cisor, and is rather less recurved. The molars have each a single 

 fang. In Stemmatopus the last upper molar has two divergent 

 fangs, at least in the young state. 



In the great proboscidian and hooded Seals (Cystophora), the 

 incisors and canines still more predominate in size over the 

 molars ; but the incisors are reduced in number, the formula here 



s 



.2.2 1.1 4.4 1.1 





The molars are single-rooted, and the incisors laniariform. The 

 two middle incisors above and the two below are nearly equal ; 



1 cxxm". p. 38. 

 VOL. III. Z 



