OCR Text |
Show 329 largest and the smallest, excluding the* most extreme examples, is one-sixth of the dimensions of the smaller and one- seventh of the size of the larger. The sexes differ considerably in size, relatively about the same as in Putorius visori) but the above generalizations are based wholly on males, and in each case on those of practically the same age, only specimens indicating mature or advanced age being used. The series of fully one hundred skulls of this species contained in the National Museum presents a considerable range of variation in details of structure, involving the general form of the skull, the relative size of different parts, and the dentition, especially the form and relative size of the last molar. In a former paper,* I had occasion to notice somewhat in detail the variations in color our American Martens present, and the difficulty of finding any features of coloration that seemed to indicate more than a single American species, or that would serve to distinguish this even from the Martens of the Old World. Dr. J. E. Gray, it is true, had already cajled attention to the small size of the last molar in the American Martens as compared with the size of the same tooth in the Old World Martens; but, as his observation was apparently based on a single American skull, and as I was at the time strongly impressed with the wide range of individual variation I had found in allied groups, even in dental characters, and also with the great frequency of Dr. Gray's characters failing to be distinctive, I was misled into supposing all the Martens might belong to a single circum-polar species, with several more or less strongly- marked geographical races. My friend Dr. Coues some months since kindly called my attention to the validity of Dr. Gray's alleged difference in respect to the size and form of the last molar, which I have since had opportunity of testing. This character alone, however, fails to distinguish Mustela foina from MusteUiamericana, in which the last molar is alike, or so nearly so that it tails to furnish distinctive differences. The size and general form of the skull in the two are also the same, the shape of the skull and the form of the last upper molar failing to be diagnostic. The second lower true molar, however, in Mustela foina presents a character ( shared by all the Old World Martens) which serves to distinguish it from Mustela americana, namely, the presence of an inner cusp not found in the latter. In Mustela flavigula, the last molar is relatively smaller than even in Mustela americana, and of the same form. Mustela martts differs in its more massive dentition and in the heayier structure of the skull, but especially in the large size of the last molar and the very great development of its inner portion. Hence, while the size and shape of the last upper molar serves to distinguish Mustela martes from Mustela americana, it fails as a valid distinction between Mustela americana and Mustela flavigula and Mustela foina. As already remarked, however, Mustela americana lacks the inner cusp of the second lower molar, which is present in the Old World Martens, or at least possesses it only in a very rudimentary condition. * " Mammals of Massachusetts", Ball. Mus. Comp. Zool., vol. i, pp. 161- 167, Oct., 1869 |