14 THE BRITISH MAMMALS : ORDERS, FAMILIES, ETC 



the right front tooth generally small, but occasionally almost as long. 

 The white whale (Delphinapterus) is white both above and below ; the 

 pilot whale, otherwise the blackfish, is black all over except a 

 whitish throat patch, and, occasionally, a narrow stripe along the 

 underparts. The killer (Oreo) is black above and white from the 

 angle of the mouth downwards, a white patch being conspicuous 

 over the eye, and is famous for the tall dorsal fin and twelve 

 pairs of large conical teeth ; the porpoise (Phoccena) is black 

 above and white below, there is no white patch over the eye, and, 

 as is well known, the triangular dorsal fin is of no great elevation, 

 and there are from sixteen to twenty-six pairs of small, spatulate 

 teeth. 



This leaves us with the dolphins, in which the beak is more or 

 less prominent. In one genus (Lagenorhynchus) it is comparatively 

 short, and the dorsal fin higher than the mouth is long. In the two 

 genera that remain the beak is more noticeable, and the mouth is 

 longer than the dorsal is high. These two are the .bottle-nose 

 dolphin (Tursiops), which has from twenty-one to twenty-five pairs 

 of teeth and no grooves in the palate, and the common dolphin 

 (Delphinus), in which there are from forty to sixty pairs of teeth, 

 a grooved palate, and a beak narrow and rather long, without the 

 gradual tapering from the head characteristic of the other. In this 

 way we have obtained 



CETACEA 



Without teeth ; with whalebone. 



1. (Balaenidae) 



No dorsal fin ; throat not grooved ; five digits in 



flippers Baltsna, 53. 



With dorsal fin ; throat grooved ; four digits in 

 flippers. 

 Flippers long, white, and scalloped Megaptcra, 



54- 



Flippers short, black or black and white 

 Balcenoptera, 55 to 58. 



With teeth ; without whalebone. 



2. (Physeteridae) 



Teeth of upper jaw rudimentary or absent. 

 Dorsal fin rudimentary Physeter, 59. 

 Dorsal fin well developed. 



Head with crests. 



Teeth in forepart of lower jaw Hypwoodon, 60. 

 Teeth, a single pair near middle of lower jaw 



Mesoplodon, 61. 

 Head without crests. 



Teeth, a single pair in front of lower jaw 

 Ziphius, 62. 



