LÖNNBERG, THE DENTITION OF DELPHINAPTERUS LEUCAS. 13 



The dental formula of Squalodon is therefore written by Abel^ 



q i c q 



in tbe following way: t ^\ c-; p ^\ m -. The number of pre- 



molars of Squalodon agrees thus almost exactly with the 

 number of teeth of Delphinapterus . It bas been pointed out 

 above that the latter possesses neither incisors nor canines, 

 and as the moJars were on the way of being reduced already 

 in the primitive whales it is hardly probable that any such 

 have remained up to the present time. In consequence of 

 this it may be assumed that all the teetb of Delphuiapterus 

 are premolars, and homologous with the same number of 

 premolars in Squalodon. When seen in this light it appears 

 more than probable that the small accessory cusps described 

 and figured above on the new and unworn small crowns of 

 the teeth of Delphinapterus are to be regarded as remnants 

 of the cusps of the teeth of the Squalodons, and it does not 

 at all appear difficult to understand how such teeth as those 

 of the former could have been derived from those of some 

 form of Squaladon through reduction of the crown^ and in- 

 creased (finally permanent) growth of the root (since through 

 fusion of the originally double roots a simple root has been 

 formed). 



There are several characters of the White whale which 

 indicate that it represents a comparatively rather low, or 

 primitive type among the now living Cetacea. Such charac- 

 ters are among others the free cervical vertebrse, the great 

 number (8) of twoheaded ribs, the lack of dorsal fin etc. To 

 those may now be added the peculiarities of the teeth de- 

 scribed above. If all these primitive characters are connted 

 together it will appear that the White whale has not reached 

 so far from its ancestors as many other toothed whales. It 

 is also quite evident from the above given description of the 

 structure and development of the teeth of Delphinapterus 

 that these teeth are something quite sui generis, totally dif- 

 ferent from the enamel-covered teeth of the typical Dolphms 

 (conf. below). Such teeth as those of the latter can never 

 be developed from such as those of the White whale. In 



^ Verhandl. Deutsch. ZooL Gesellschaft in Breslau 1905. Leipzig 

 1905. p. 89. 



^ The reduction or degeneration of the crown is proved by the great 

 thinness of the enamel covering; as recorded above. 



