REPORT ON THE SEALS. 71 



Trichechus (Odobwnus) rosmarus, Linnaeus. Morse, Walrus, or Sea Horse. North 



Atlantic and Pacific Oceans. 



Odobxnus rosmarus, Linn., Syst. Nat., ed. i., 1735. 



Phoca rosmarus, Linn., Syst. Nat., ed. x. p. 38, 1758. 



Trichechus rosmarus, Auctorum. 



Odobsenus rosmarus, Steenstrup, Ofversigt k. Vetensk. Akad. FdrhandL, Bd. xvi. p. 441, 1859; 



Zeitschr. f. gesaramt. Natunv., xv. p. 275, 18G0. 

 „ „ Malmgren, Ofversigt k. Vetensk.-Akad. Forhandl., 1863 (1864) (quoted by 



Allen). 



The above description of the skull of the genus Trichechus has been written from the 

 comparison of the crania of a number of specimens in the Anatomical Museum of the 

 University of Edinburgh, which are all believed to be from the North Atlantic Walrus, 

 so that they may be regarded as comprising both its specific and generic characters. On 

 the supposition entertained by the majority of naturalists that the Walruses of both the 

 North Atlantic and North Pacific are of the same species, they would, I doubt not, also 

 coincide with the last-named animal, but as I have not had the opportunity of examining 

 the skull of a specimen known to be from the North Pacific I cannot speak with absolute 

 certainty. Mr. J. A. Allen has indeed attempted to show that specific differences separate 

 the Walruses of these two oceans from each other, and, reviving an old name given by 

 Illiger, he has distinguished the North Pacific animal by the name of Odobmms (Triche- 

 chus) obesus. In thus subdividing the genus he is also supported by Mr. H. E. Elliott. 



In making this division Mr. Allen attaches great importance to a difference in the 

 relative development of the frontal and occipital regions in the two animals. In the 

 Atlantic species, he says, the narrow facial breadth is in striking contrast with the great 

 occipital breadth, whereas in the Pacific species the two regions are more equally 

 developed. The interorbital constriction is both relatively and absolutely much narrower 

 in the Pacific animal ; the tusks are longer and thicker, generally more convergent and 

 less incurved in the Pacific, whilst in the Atlantic animal they are divergent and strongly 

 incurved. In the Pacific species the front profile is nearly vertical, and the anterior 

 edge of the nasals is very little posterior to the front border of the base of the tusk, and 

 the orbits are more anterior ; in the Atlantic animal the front profile is very oblique, 

 the muzzle is smaller and the nasals scarcely pass beyond a vertical line drawn from the 

 hinder border of the base of the tusk. 



With regard to these characters I would point out that the increase in frontal breadth 

 of the North Pacific animal, which makes it approximately equal to the occipital breadth, 

 would necessarily be occasioned by an increase in thickness of the canine tusks, and 

 the consequently greater development of the superior maxillary bones for their lodg- 

 ment, and as it is stated that in the Pacific animal the tusks are thicker than in the 

 Atlantic specimen, it is possible that these differences, as described by Allen, are not 

 specific, but are simply due to certain specimens having thicker tusks than others. With 



