THE SPECIES OF THE GENUS. 19 



Pexistence de deux especes de morses."* Fremery, in 1831, 

 having before him a series of eleven skulls, distinguished three 

 species, namely, Trichechus rosmarus, T. longidens, and T. cooki. 

 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 

 tittle 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-thirds 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 tighter 

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

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

 Cook), already noticed, and hence is the same as Utiger'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 skull 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 Mammif eres, p. 235. 



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

 observes as follows respecting probable sexual and individual differencea 

 in the tusks and skulls of Walruses: "Hr. Fremery ftilirt an, dass Hr. 

 Temminck einen (naeh Deutlichkeit der Nahte) noch jungen Schadel des 

 Keichsmuseums mit ausgezeichnet langen diinnen Stosszahnen fur den 

 eines Weibchens gehalten habe. Ich erinnere mich auch von Gronlands- 

 fahrern gehort zu haben, dass sich das Weibchen durch langere, diinnere, 

 dass Mannehen durch kiirzere, aber viel dickere Stosszahne auszeichne." The 

 alleged difference in the specific gravity of the bones of the skull he be- 

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

 ber of molar teeth. Respecting the prominence of the lower border of the 

 nasal opening he says: "Die inehr oder minder starke Hervorragung dea 

 unteren Randes der Nasenoffnung kann ich dagegen nur fur eine individuelle 

 Verschiedeuheit halten, da ich sie bei einem Schadel mit kurzen Stoss- 

 zahnen, der die ubrigen. vom Verf. hervorgehobenen Merkmale besitzt, sehr 

 stark, und umgekehrt bei einem alten Schadel mit langen Stosszahnen kaum 

 merklich finde." Archiv fur Naturgesch., 1838, pp. 128, 129. 



