216 PROCEEDINGS OF THE ACADEMY OF [1894. 



Prof. Baird's description of mar/ixter aims to distinguish it from 

 all forms of the genus known to him by its large size and massive, 

 rounded molars. So far as I have examined the species of Ncotoma 

 now known, and which number five times as many as were recognized 

 in Baird's day, I find maglder to be somewhat larger than any other. 

 It has a comparatively short tail, but the length and girth of body 

 considerably exceeds that of other species whose total length may 

 average more than in a series of magister. It is a satisfaction to thus 

 confirm the appropiiateness of Baird's specific name. As to its 

 cranial characters, magider presents us with the largest skulls I have 

 examined in this genus, but the comparative size and shape of the 

 molars as given by Baird cannot be said to be diagnostic. It is 

 probable when Prof. Baird made these comparisons he only possessed 

 specimens of old individuals, in which this peculiarity of the molars 

 is always apparent, and does not vary to any great extent among 

 specimens of N. fuscipes, floridami , or cinerea of same age, and is of 

 the same general character in all. The same may be said of the fold- 

 ing and indentations of the enamel in very old specimens. Younger 

 specimens of maglder, both fossilized and recent, show a very close 

 resemblance in tlieir molar dentition to fioridana and cinerea of 

 same age. The incisors and rostral portion of the skull in magider, 

 however, are much wider and heavier than in any other Neotoma I 

 have seen. Compared with N. Jioridari,a (to which magider both 

 physically and geographically shows the closest alliance) it may be 

 noted from the table of measurements that the recent and fossil crania 

 of the cave rat are much larger than in the wood rat. In super- 

 ficial proportions the difference is less apparent, but in the following 

 particulars their divergence is constant and specific : — 



1. The post- palatal notch of magider is acuminate, often sharply 

 so, at other times hearing in its aj>ex a minute, blunt point, 

 directed posteriorly ; in fioridana the post-palatal margin is broadly 

 and evenly rounded or nearly square cut between the opposing last 

 molars, the pterygoids being more divergent and i-elatively shorter. 

 2. In magider the slits separating the palatal from the sphenoid bones 

 are often nearly anchylosed ; in fioridana they are more widely sepa- 

 rated. 3. The interorbital depression and supraorbital ridges of the 

 frontals in younger specimens oi' magider are very decided ; in fioi'i- 

 daiia nearly obsolete. 4. As above stated, the greater relative 

 breadth of incisors, maxillaries, and njisals in magister. 



