UPPER JAW. M. Length of true molar series ·036 Length of last molar ·0135 Width of last molar ·015 Length of second molar ·012 Breadth of second molar ·015 Length of first molar ·0105 Breadth of first molar ·012 Length of last premolar ·009 Breadth of last premolar ·011 Length of third premolar ·008 Breadth of third premolar ·009 LOWER JAW. Length of true molar series ·042 Length of last molar ·018 Breadth of last molar ·009 Length of second molar ·013 Breadth of second molar ·008 Length of first molar ·012 Breadth of first molar ·008 Length of third premolar ·008 Breadth of third premolar ·005 Diameter of canine at base ·006 Length of symphysis (about) ·027 Found at Henry's Fork. ARTIODACTYLA. GENERA INCERTÆ SEDIS. ITHYGRAMMODON, _gen. nov._ Our fragments of this fossil show an animal about the size of the llama, and approximating more closely to the _Tylopoda_ than to any living forms. The genus is established upon the two premaxillary bones, containing the incisors, parts of the maxillaries, the canine and the first premolar; besides fragmentary portions of the palatine plates. As the peculiar features of these remains render them unique, we are warranted in establishing the genus _Ithygrammodon_. _Generic characteristics._ The premaxillaries are long, narrow, and very straight, bent slightly in on their own axis as in _Camelidæ_, but expanded laterally at the end of symphysis as in _Pecora_. The upward processes are sharply defined, with a wide, rounded upper border. The upper incisors are six in number, and _are placed nearly in a straight line fore-and-aft_, separated from each other and from the canine by small and subequal diastemas. The _incisors_ are nearly equal in size, cylindrical in shape, are placed vertically in their alveoli, and are slightly recurved. The spine of the premaxillaries is long and thin, giving very long anterior palatine foramina, as in _Ruminantia_. The premaxillaries, in position, are close together, showing a very narrow muzzle.