428 ZOOLOGY. 



fig. 1) the genus would rest upon the presence of two dorsal prominences, 

 one situated near the fin and the other near the head. The form of the 

 snout is unknown, so that we are in doubt as to whether it is elongated as in 

 the dolphin, or truncated as in porpoises. The naturalists of the "Uranie" 

 met a second species in 1819, between the Sandwich Islands and New South 

 Wales, in 5° 28' north latitude. This is known also under the name of 

 0. rhinoceros. 



Fam. 4. Heterodontid^, is diflicult to characterize on account of the 

 dissimilarity between the few genera and species of which it is composed, 

 and the little knowledge possessed of them. The teeth are of different sorts, 

 always few in number, and sometimes even wanting in the adult state. 



The extinct genus Ziphius^ which we place here for the sake of conveni- 

 ence, is intermediate between Hyperoodon and Physeter, and seems to have 

 preceded and foreshadowed in the tertiary epoch these two genera of our 

 days. Three European species are described, but none of them are fully 

 known. 



The genus Hyperoodon is based upon a singular structure of the head, 

 which consists of a large and elevated apophysis rising from the middle of 

 each upper maxillary, giving to the posterior part of the head that peculiar 

 shape which chaT-acterizes it. Their teeth, two in number, small, acute, 

 near the extremity of the jaw, sometimes hidden under the gum or wanting, 

 whence the name of Delphintis edentulus, and the generic appellation of 

 Aodon. The absence of teeth has led some others to place this animal 

 among whales proper, but as it has no whalebones others have been 

 induced to bring it nearer the dolphins. Only one species is described as 

 belonging to this genus, the //. haussardii from the northern European 

 seas. It has a darsal fin and small pectorals. The beak is detached from 

 the forehead, which is rounded and abrupt. The eyes are quite distant 

 from the angles of the mouth, a peculiarity which distinguishes it from 

 the dolphins proper. The body is fusiform, and tapers rapidly away from 

 the dorsal fin to the tail. 



The genus Heterodon must provisionally include the two-toothed cachalot 

 of Sowerby {Physeter hidens soiverhyi, Dewh.), which we shall designate by 

 the name of U. soiverhyi. Its characters consist of a narrow and elongated 

 snout, the upper jaw longer than the lower, which receives it; one single 

 tooth below on each side, compressed, and obliquely directed backwards, 

 placed in the middle of the margin of the jaw. A blow-hole, crescent- 

 shaped, with the concavity forwards. This species was observed on the 

 coast of England. The two-toothed dolphin {Delphinus hidens) resembles 

 the Hyperoodon by the form of its head. Its place is, at any rate, in this 

 family ; but whether it belongs to the genus Hete)-odon^ or to any other, 

 we cannot decide at present. 



We place here the genus Arnanaais of Lacepede, created for one species 

 of cetacean, called by the Greenlanders Arnancdc, from the supposed purga- 

 tive qualities of its flesh and fat. It has also been referred to the genus 

 Monodon, and is the M. spurms of the " Encyclopedic Methodique." The 

 Amanicus grcenlandicus has one or two small obtuse, conic, and crooked 

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