122 



t'estooiiR both intcrnall}' and extemall\'. The inner side of the crown is 

 defined from the back border by an acute ridge. 



The crown of the last; premolar has the same constructioii as that in advance, 

 but is sliorter and wider. The heel is slightly wider and more excavated, but 

 the fore part of the basal ridge is not so prominent. The ridge defining the 

 inner side from the posterior border is slightly more advanced and prominent, 

 and the surfaces it separates are more concave. 



The crowns of the true molars are nearly alike in form and size, though 

 the first is in a trifling degree more prominent and wider. They have the 

 same general constitution as those of shrews, of the hedgehog, the galeopi- 

 thecus, and the opossum. Eacli is composed of two divisions, of which the 

 posterior is the larger. The anterior division consists of a small, outer demi- 

 conoidal lobe, with aV-like summit joining by its arms a pair of inner and smaller 

 pyramidal lobes. The posterior division consists of an outer lol)e like that in 

 advance, but larger, and joining it by one of the arms of its V-like summit, 

 while the other arm joins a small pyramidal lobe at the inner corner of the 

 crown. The outer part of the base of the crown is embraced by a basal cin- 

 gulnm nearly half its depth. 



The space occupied 1))^ the teeth, in the view that there were two incisors, 

 a canine, and six molars, is 74- lines. The last two premolars and the suc- 

 ceeding two molars occupy a space of 4.6 lines. 



PALiEACODON. 



Pal^acodon veeus. 



Two small fossil specimens, discovered the previous, summer by Dr. Carter 

 at Lodge-Pole Trail, Wyoming, indicate an insectivorous animal, or, perhaps, 

 a marsupial allied to the opossum. One of the specimens consists of an 

 nppcr-jaw fragment containing a molar, which appears to be the penultimate 

 one of the series; the other is an isolated tooth, perhaps the last upper pre- 

 molar or first molar. 



The jaw-fragment is the portion which forms the anterior abutment of the 

 zygoma. In advance of the tooth it retains are the remains of the alveoli of 

 two others, and behind it the remains of another. 



Tlie molar of the jaw-fragment is represented in Fig. 46, Plate VI, magni- 

 fied four diameters. The crown bears some resemblance with that of the 

 molars of tiic opossum, ])ut is less narrowed internally, and is therefore more 



