Mr Gibson on the Skull of a Narwhal. 257 



III. On the Skull of a Narwhal (Monodon monoceros, Linn.), 

 with two fully-developed Tusks. By John Gibson, Esq. 

 The author, after referring to the dentition of the Cetacea 

 in general, and of the narwhal in particular, drew attention 

 to the occasional presence in the male of two fully-developed 

 tusks. That these are of rare occurrence may be gathered 

 from the fewness of the bidental skulls which are known to 

 exist, notwithstanding the assertions of whaling captains that 

 they occasionally see such specimens from their ships. The 

 appearance to which they refer may, as has been suggested, be 

 due to the presence of two male narwhals in close proximity 

 to each other, their tusks alone being visible above water. 

 According to a recent authority, there were in 1871 only nine 

 authentic specimens know^n in Continental collections, four of 

 which were in Copenhagen. In Great Britain there w^ere only 

 two — a complete skeleton, with bidental skull, in Cambridge 

 University Museum, the right tusk of which measured 6 ft. 1 in. 

 in length, and 8-f in. in girth at the outer edge of the socket ; 

 and the left tusk, 6 ft. 7 in. in length, and 9-|- in. in girth. 

 The shorter tusk had evidently been broken at the tip, so 

 that probably the tusks had been originally of about equal 

 length. The other British specimen w^as that of a young 

 narwhal in the Hull Museum, in which the left tusk measured 

 20 in. in length, and the right tusk \ in., exclusive of the 

 portion within the skull. During a recent visit to the 

 museum in Dundee, the author had his attention drawn to a 

 splendid bidental skull which had been shortly before pre- 

 sented to that institution by Captain Graville of the "Camper- 

 down," who had obtained it in the seal fishery grounds off the 

 coast of Greenland. The following are the measurements of 

 this, the only specimen of the kind in Scotland, for which I 

 am indebted to the kindness of Mr J. Maclauchlan, the 

 curator of the Dundee Museum : 



Total length of skull, exclusive of tusks, . . , . 1 ft. 1 Of in. 



Greatest breadth across squamosals, . . . . . 1 , , 3 



Breadth at narrowest part where the tusks are exserted, . ,, 5f 



Length of left tusk, 6 ,, li 



right tusk, 5 „ 7i 



Girth of left tusk at edge of socket, . . . . • ,, 7f 



right ,, ,, ,, 6| 



