| OCR Text |
Show 339 Measurements of seventeen skulls of URSUS AMERICANUS. H 3934 1155 1156 987 1154 988 3894 3798 2350 994 993 991 12398 3650 6949 8695 9477 I Locality. Key Biseayiie, Fla PrairieMerItooge, La . . . . . . . . . . . . . . . . . . . .. . . . . . . d o . . . . . . . . . r. do do d o . . . . . . . . . Georgia New York do Copper Mines, N. Mex . . . . " d o . . . . . . . ' . - -. do Alaska do & d-i 13.10 13.90 12.70 13.50 11.10 10.60 11.15 11.80 11.00 9.90 11.35 11.75 11.40 12.15 10.30 10.35 10.07 Width. 7.40 7.45 7.35 6.10 5.95 6.10 7.35 7.55 6.07 7.05 6.85 7.40 7.40 6.00 6.30 5.15 Remarks. Very old. Do. Do. Do. Middle- aged. Bather young. Middle- aged. Very old; brown. Do. Very old; black. The range of variation not dependent upon locality is more fully indicated in the table of detailed measurements of these skulls given below, but certain of the most prominent points of variation are not well shown by any series of measurements. Especially is this the case in respect to the amount of convexity different specimens present, in which individual variation is strongly marked. One of the most prominent distinctions of U. americanus as compared with U. arcios and its varieties is the great convexity of the upper ontline of the skull, both antero- posteriorly and transversely. Another feature is the constriction of the facial portion, giving a concave outline to the nasals when viewed in profile. But there are exceptions, even to the first of these distinctions, one or two specimens occurring ( especially No. 2250 from New York) in which the flattening of the frontal region is as marked as in average skulls of XT. harribilis. This flattening is also well marked in Nos. 1155 and 1156, from Louisiana. The greatest convexity is reached in No. 3484, from Key Biscayne, Fla.; this and No. 2250 ( New York) presenting the two extremes in respect to convexity. No. 3£ 94, from Georgia, has about the same degree of convexity as the Florida specimen. No. 2250 is also remarkable for the shortness of the facial portion of the skull, thereby imparting to it a greater than the nsual ratio of width to length. In this specimen ( mentioned by Professor Baird as remarkable for its width*), the width is 0.69 of the length. In another, from Louisiana ( No. 1155), it falls as low as 0.54! The average ratio of width to length is about 0.56 to 0.60. The teeth of U. americanus seem, in looking at them, to be relatively much smaller than in V. arctas, but, updu careful measurement, the difference is quite small, while they are of the same relative size as those of U. horribili8. In U. americanus, the temporal ridges pass more abruptly inward toward the medial line of the skull than in either U. harribilis or U. aretos. The most important distinction presented by U. americanus is the form of the last upper molar. In O. americanus, the crown is widest at the middle, narrowing both anteriorly and posteriorly, but most rapidly posteriorly. The inner border is nearly straight; the outer has a prominent medial convexity, while in U. harribilis and U. arctas both outlines are nearly straight and generally about equally convergent. In U. americanus, the anterior third of the last - molar is generally narrower * Mam. N. Araer., p. 227. |
