THE SPECIES OF THE GENUS. 19 



I'existeuce cle deux esp^ces de morses."* Freiaery, in 1831, 

 having before liim a series of eleven skulls, distinguished three 

 species, namely, Tricheehus rosmartis, T. longidens, and T. cooM. 

 The first {T. rosmarus) was principally characterized by having 

 diverging tusks, about as long as the length of the whole head, 

 faintly grooved on the outside, and with two distinct grooves on 

 the inside ; by the possession of five back teeth, the last two 

 very small ; by the lower edge of the nasal opening being but 

 little produced ; by the occipital crest being strongly developed ; 

 and by the great specific gravity of the bones of the skull. The 

 second [T. longidens) was principally characterized by the tusks 

 equalling or exceeding in length two-thu'ds of the length of the 

 skull, with a single deep groove on the inner side ; by having 

 only four back teeth, the last one small; a smaller develop- 

 ment of the occipital crest {except in old animals !) ; and a lighter 

 specific gravity of the bones. The third (T. cooM), considered 

 as a doubtful species, was based wholly on Shaw's plate 68 (from 

 Cook), already noticed, and hence is the same as Illiger's T. 

 divergens. Wiegmann, von Baer, Stannius, and most subsequent 

 writers, have properly regarded Fremery's characters of his T. 

 rosmarus and T. longidens as based merely on ordinary indi- 

 vidual or sexual differences. Wiegmann, and also Temminck, 

 according to Fremery, believed the female to be distinguishable 

 from the male by its longer and thinner tusks, with the crests 

 and ridges of the skidl less developed, while other differences, 

 as the relative prominence of the bony lower edge of the nasal 

 opening, were differences characteristic merely of different indi- 

 viduals.t Stannius, however, in 1842, after passing in review 



* Dents des Mammif6res, p. 235. 



t Wiegmann, in commenting upon Fremery's supposed specific differences, 

 observes as follows respecting probable sexual and individual differencea 

 in tbe tusks and skulls of Walruses: "Hr. Fremery fiibrt an, dass Hr. 

 Temminck einen (nacli Deutlicbkeit der Nahte) nock jungen Sckiidel des 

 Eeicksmuseums mit ausgczeichnet langen diinnen Stosszakuen fiir den 

 eines Weibckens gekalten kabe. Ick erinnere mick auck von Gronlands- 

 fakrern gekort zu kaben, dass sick das Weibcken *durck langere, diinnere, 

 dass Manncken durck kurzere, aber viel dickere Stosszakne auszeickne." Tke 

 alleged difference in tke specific gravity of tke bones of tke skull ke be- 

 lieves also to be a sexual feature, as possibly also tke difference in tke num- 

 ber of molar teetk. Eespecting tke prominence of tke lower border of tke 

 nasal opening ke says: "Die mekr oder minder starke HervoiTagung des 

 unteren Eandes der Nasenoffhirng kann ick dagegen nur fiir erne indi^dduelle 

 Versckiedenkeit kalten, da ick sie bei einem Sckadel mit kurzen Stoss- 

 zaknen, der die iibrigen vom Verf. kervorgekobenen Merkmale besitzt, sekr 

 stark, und umgekekrtbei einem alten Sckadel mit langen Stossziiknen kaum 

 merkkck finde." Archiv fiir Naturgesch., 1838, pp. 128, 129. 



