9. HALICYON. -9 



trarj-, the angle of the lower jaw is more towards the front, and the 

 hinder edge of the ramus ascends obliquely, with the notch consider- 

 abl)^ in front of the condyle (see c, tig. 9). — P. Z. IS. 1864. 



The skull of Halicyon resembles that of Cullocej)halus hispidus and 

 Pagophilus Onmlandkus in the dilatation of the front part of the 

 lower edge of the lower jaw ; but it agrees with Calloceplialus his- 

 pidus most in the greater development of the face, and in the concave 

 edge of the hinder part of the palate. 



It differs from these skulls — 



1. In the dilatation of the lower jaw not being extended so far 

 back, only occupying the first two-fifths of the length of the jaw ; 

 while in the other two species it occupies full half the length of 

 that bone. 



2. In the sides of the lo-^^er jaw being much wider apart, and 

 arched outwards, making the space between them much wider be- 

 hind, agreeing in this respect with Phoca barhata. 



3. In the front of the lower jaw being thick and swoUen, and 

 with only a slight ridge on the middle of the lower edge in front ; 

 and the jaws in this part being weU separated from each other, not 

 thin, concave inwardly, and with a well-developed inferior edge on 

 the inner sides, those of the two sides of the jaws being parallel and 

 near together in the centre. 



The angle at the hinder lower edge of the lower jaw is much 

 more produced, and with a more prominent tubercle, than in either 

 Calloceplialus hispidus or Pagophilus Groenlandicus. 



4. The hinder edge of the palate being concave forwards, and not 

 straight and transverse as in Pagophilus, nor angularly cut out as in 

 Callocephcdus. — Gray, P. Z. S. 1864. 



In the younger specimen the edge of the jDalate has a slight pro- 

 minence in the middle of each side ; but this is evidently an acci- 

 dental deformity, as the prominences are not of the same size in the 

 two sides. In the advilt skull the two sides of the palate are evenly 

 arched out. 



The lower jaw most resembles that of the restricted genus Phoca 

 (of which P. barhata is the type) in being solid and strong, and in 

 the two sides being arched out, leaving a very wide oval space be- 

 tween them, the front part of the space being continued by a 

 tubercle on the inner edge of the front of the jaw, a short distance 

 from the symphysis. 



In Phoca the tubercle on the inner side of the lower edge is short, 

 rounded, blunt, and more or less rugose ; in the new Seal, HaUcyon, 

 it is a short-edged, elongated ridge. In Phoca the teeth are small, 

 erect, and fai' apart ; in Ucdicyon they are larger, closer together, and 

 distinctly three- or five-lobed. 



In Halicyon the hinder edge of the ramus of the lower jaw is simple, 

 with a distinct notch between it and the tubercular angle of the jaw. 

 In Phoca the hinder edge of the ramus is inflected, forming a large 

 half-oblong lobe, convex in front and concave behind (6, fig. 9). 



It is very interesting to observe that there is a representative 

 genus on each side of the Arctic Pole; and this agrees with my 



