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 Syperoo- 

 dontina ; 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 con- 

 spicuous over the orbit, while in true dolphins it is comparatively 

 covered by the lateral dilation 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 doljjhins, it is to be 

 observed that if the Catodontidce iovm a group of value equivalent 

 to that of Belphinidce, the sperm whales, and particularly the 

 Euphysetes, can be only aberrant forms connecting the first- 

 mentioned group with the dolphin family. It must 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 

 BalcBnidee or family of right whales. 



