42O 



ORDERS OF MAMMALIA. 



wise, that the ear-bones or " cetotolites " which occur in the 

 Red Crag (Pliocene) are, in some instances at any rate, refer- 

 able to members of the Baltznidce. 



Fam. 2. Catodontidce. The family of the Catodontidce, or 

 Physeterida, comprises the Sperm Whales or Cachalots, with 

 which we commence the series of the Toothed Whales (Odon- 

 toceti). They are characterised by the fact that the palate is 

 destitute of baleen plates, and the lower jaw possesses a series 

 (about fifty-four) of pointed conical teeth, separated by inter- 

 vals, and sunk in a common alveolar groove, which is only im- 

 perfectly divided by septa. The upper jaw is also in reality 

 furnished with teeth but, with a single partial exception, these 

 do not cut the gum. 



Remains of Cachalots (Physeter) occur in the Pliocene and 

 Post-Tertiary deposits, and their existence has even been indi- 

 cated in the Miocene Tertiary. They are, however, of no 

 special importance. 



Fam. 3. Delphinida. This family includes the Dolphins, 

 Porpoises, and Narwhal, and is characterised by usually pos- 

 sessing teeth in both jaws ; the teeth being numerous, and 

 conical in shape. The nostrils, as in the last family, are united, 

 but they are placed further back, upon the top of the head. 

 The single blow-hole or nostril is transverse and mostly cres- 

 centic or lunate in shape. The head is by no means so dispro- 

 portionately large as in the former families, usually forming 

 about one-seventh of the entire length of the body. 



Fig. 348. The common Dolphin (Delphinus delphis). 



The genus Delphinus, comprising the common Dolphins, 

 appears to date from the Miocene Tertiary, and is well repre- 

 sented in deposits of Pliocene age. In Miocene strata also 

 occur the Delphinoid remains which have been referred to the 

 genera Stereodelphis and Champsodelphis. 



Fam. 4. Rhynchoceti. This family is allied to the Cacha- 

 lots or Sperm Whales, and includes the so-called " Ziphioid 

 Whales." They are distinguished by the possession of a 



