442 MONOGRAPHS OP NORTH AMERICAN RODENTIA. 



pean skulls. Dr. Ely stales that, in six American skulls, the average length 

 is 5.39, and the average length of 1 lie nasals 1.81, or nearly 0.34 of the length. 

 In three others, with an average length of 4.42, the nasals average 1.59 or 

 0.36 of the length. In seven others, he finds, however, the relative length 

 of the nasals still greater. 



"(5) The frontal portion of the lachrymal bone in the American Beaver," 

 Brandt finds, "is more triangular, — posteriorly twice as broad as anteriorly, — 

 and smaller than in the European-; it is also nearly limited to the space 

 between the malar and frontal bones; since it impinges only with its anterior 

 border-like narrow end upon a small process of the upper jaw, or even only 

 approaches it. In the Beavers of the Old World, however, the larger, more 

 quadrangular, anteriorly and posteriorly equally broad frontal portion of the 

 lachrymal bone lies not only between the malar and frontal bones, but is 

 united in similar extent equilaterally with the superior maxillary." 



In the majority of instances, Dr. Ely finds the differences here men- 

 tioned by Brandt, but states that in some of his skulls the lachrymal has the 

 quadrangular form, being as broad anteriorly as posteriorly, and my own series 

 affords additional exceptions, the individual variation in the form of this bone 

 being very great in the American skulls. 



In respect to the anterior aspect of the skull, Dr. Brandt found the 

 nasal opening triangular in the European, — narrower interiorly, and hence 

 more or less pointed, — but quadrangular in the American, being but little 

 narrower below than above. Dr. Ely notes the greater tendency to the 

 quadrangular form in the American, but cites examples where the opening 

 is nearly if not quite as triangular as in the European, and I find several 

 American skulls in my series that fully bear out the statement. The form of 

 the nasal opening, however, is very variable; in very few is it distinctly quad- 

 rangular, being generally considerably narrowed and rounded, or more or less 

 angular, below. Dr. Brandt also finds the inter- and inferior mamillaries 

 broader in the European skulls than in the American, and the incisors also 

 correspondingly broader. As shown by Dr. Ely, however, the difference is 

 evidently somewhat less than the amount claimed by Dr. Brandt. 



In respect to the lateral aspect of the skull, Dr. Brandt finds no differ- 

 ence in the dorsal outline in the two forms, but points out a number of alleged 

 differences in other features. The zygomatic process of the maxillary he 

 claims is relatively narrower, as compared with the malar bone, in the 



