60 



But if such be the series of natural affinity among the true 

 dolphins^ it must be confessed that it is very difficult to discover 

 good characters, founded on the skeleton, by which sperm 

 whales can be excluded from the group. It is very clear that 

 our two Sydney whales described in the preceding chapters 

 touch the above series at some point between Platanistina and 

 Hyperoodontina ; for they have the toothless upper jaw of the 

 latter tribe of dolphins, and that long symphysis of the under 

 jaw which is so remarkable in the fresh water dolphins, while 

 a crest is formed by the elevation of the maxillary bones in all 

 the three groups. The difference is that in all the dolphins of 

 the above series the base of the maxillary is extended laterally 

 over the frontal, whereas the base of the maxillary in 

 sperm whales is extended more behind for the purpose of 

 aiding to form the spermacetic cavity. In all dolphins the 

 nostrils approach to equality and symmetry, whereas in the 

 family of sperm whales the nostrils are exceedingly unequal 

 and unsymmetrical — and thus have a peculiar location in respect 

 to the distorted and dislocated nasal bones. In the Catodontidce 

 also, the frontal bone is very conspicuous over the orbit, while 

 in true dolphins it is comparatively covered by the lateral 

 dilatation of the maxillary bones. Again a very remarkable 

 distinction is this, that the toothed edges of the upper and 

 under jaws in all dolphins are parallel, whereas in sperm whales 

 the sides of the under jaw are linear and laterally compressed 

 from where the symphysis takes place ; and the tapering upper 

 jaw is thus very much broader than the under. 



Although such are perhaps the most valid characters by which 

 sperm whales can be separated from marine dolphins, it is to 

 be observed that if the Catodontidce form a group of value 

 equivalent to that of Delphinidce, the sperm whales, and parti- 

 cularly the EtiphyseteSy can be only aberrant forms connecting 

 the first -mentioned group with the dolphin family. It musi^ 

 be granted also on this hypothesis that the researches of 

 naturalists have not as yet made us acquainted with the 

 normal form of Catodontidce, nor yet with those species of the 

 group that pass off to the Balcenidce or family of right whales. 



