MUSEUM OF COMPARATIVE ZOOLOGY. 191 



Baird not having then received the Saranac (New York) specimen, with 

 the breadth of the head seventy-one per cent of the length. In five skulls 

 of the U. arctos, of which measurements are given by Dr. Gray, the aver- 

 age proportion of breadth to length is sixty-seven per cent ; in five of the. 

 U. "torquatus," sixty-one; in two of U. "syriacus," sixty; in four of U. 

 " Isabellinus" sixty. The average of these sixteen European and Asiatic 

 skulls is thus sixty-two per cent. Gray also gives measurements of five 

 American skulls ; viz., two of U. cinereus (= U. liorribilis Ord) and three 

 of U. " americanus "; the proportional breadth of the skull in the latter is 

 sixty-one per cent, and in the former fifty-eight. This would seem to 

 indicate a tolerable constancy in the greater narrowness of the skull in the 

 American bears. But from MiddendorfTs table of measurements of fifty- 

 five skulls, from different parts of Russia (chiefly from Northeastern Asia), 

 the percentage of breadth to length falls to fifty-eight and a quarter, and 

 is hence almost precisely that of the American. The maximum breadth 

 of skull seems to be reached in Western Europe, ; thence eastward to 

 Kamschatka there is a nearer and nearer approximation in this character, 

 as in general appearance, to the American animal. 



In respect to the variability of the skull in other particulars, Dr. Gray, 

 in referring to two skulls of U. liorribilis, remarks that they differ very con- 

 siderably ; the one is much broader, with the palate wider, the nose shorter, 

 and the orbits higher and rounder. 



In comparing the teeth of the American bears with those of the Euro- 

 pean, when but a single example of each is taken, the differences may be 

 considerable, so great, indeed, that if constant they might be regarded as 

 sufficient to decide the question of the distinctness of the species ; but since 

 specimens frequently occur from the same locality that differ as much, and 

 others from the different continents that are almost or quite indistinguish- 

 able, the unreliability of such distinctions becomes sufficiently apparent. 



Variation in the size and shape of the molar teeth are found in other 

 groups than the bears, though rarely perhaps so great. According to Pro- 

 fessor Peters of Berlin, in the Otariai, or eared Seals, the variation in this 

 respect seems to be even somewhat greater. Most authors have heretofore 

 looked upon the teeth of the Otariai as affording good generic characters, 

 but Professor Peters has found them to be so exceedingly variable that he 

 does not consider them reliable for even specific distinctions * 



The ears, in length and form, are found to vary greatly in specimens 

 of U. liorribilis from different localities, especially from points on different 

 sides of the Piocky Mountains ; whether variations of this sort are found in 

 U. arctos, it is difficult from the few sufficiently detailed measurements given 

 by authors to determine. That such do occur in specimens of bears referred 

 * Monatsber. Ak. Wiss., Berlin, 1866, pp. 261-2S1 and 635-072. 



