18G9.J 91 [Cones. 



The upper incisors, besides being larger, show a difference in the 

 position of the groove, which runs between the inner and middle, 

 instead of along the middle third of the tooth. Except in being pro- 

 portionally larger, the molars show little difference; but, age for age, 

 the transverse oval pits appear rather shallower. 



The difference in the " zygomatic processes of the temporal bones " 

 (i. e., of the squamosal), given by Audubon and Bachman, has no 

 existence in any of the numerous specimens compared; these processes 

 having as nearly as possible the same shape. That of palustris is 

 absolutely larger, proportionately to the greater size of the whole 

 skull. 



The malar is longer, and also stouter; its greater length is chiefly 

 due to development of both anterior and posterior processes; the 

 point of the latter reaches half way from the zygomatic spur of the 

 squamosal to the tympanic orifice. Notwithstanding the very appre- 

 ciable difference in the size of the external eye, the bony orbits show 

 little discrepancies in size. There is, however, a singular difference in 

 the upper border of the orbital cavity. In sylvaticus the postorbital 

 processes of the frontal have the form of slender spicula directed 

 backward, touching the parietals at their extremities, transforming 

 what would otherwise be a deep notch into an actual oval foramen on 

 either side of the frontal; in palustris, both notch and foramen usually 

 disappear by blending of this process with the frontal; sometimes, 

 however, a minute opening remains. Similarly, the anteorbital pro- 

 cesses in sylvaticus form a deep transverse notch, of which only a trace 

 exists in palustris. The median anterior extremity of the frontal is 

 prolonged in a point further between the nasals; while the posterior 

 extremities of the latter are also more acutely pointed, and run further 

 up on either side of the frontal. The slender nasal process of the 

 intermaxillary is longer. _ The base of the skull is both relatively and 

 absolutely broader, in consequence of the size and lateral projection 

 of the paroccipital. 



The form of the lower jaw, no less than the size of the incisors, 

 would seem to indicate greater masticatory power. The various 

 ridges and roughened depressions for muscular attachment are better 

 pronounced. The angle of the jaw has more sweep, and extends 

 further backward; the coronoid process is higher, wider, and more 

 upright. 



The skull of a full grown and mature (as shown by the dentition), 

 but not an old animal, exhibits the following condition of the several 



