408 O. C. Marsh — .Description of Miocene Mammalia. 



of elevations on the frontals, and a third pair on the maxilla- 

 ries. With these were elongated canine tusks. The structure 

 of the feet, also, was determined. 



The horizon was subsequently stated to be a distinct one, 

 just above the Oreodon beds, and was named by Wortman the 

 a Protoceras beds." 



In the Palaeontology of von Zittel (vol. iv, pp. 405-407), 

 figures of the type specimen of Protoceras are given, reduced 

 from the original drawings represented on Plate YII of the 

 present article ; also figures of the male skull and the feet, 

 taken from Osborn and Wortman's paper. 



JElotheriura crassum, Marsh.* 



The type specimen of the present species was discovered by 

 the writer in August, 1870, in the lower Miocene of Colorado, 

 but was not described until 1873. It was found associated 

 with a skeleton of Brontotherimn, aud thus its horizon was 

 definitely determined. A second specimen was secured in the 

 immediate vicinity, and in the same stratum. Researches in 

 the same region during several succeeding years brought to 

 light a number of other specimens, including several skulls 

 and portions of the skeleton of this and other allied species. 



Explorations begun by the writer in 1874, in Nebraska and 

 Dakota, resulted in finding several additional specimens, and 

 others have since been obtained in the same region during the 

 explorations made for the U. S. Geological Survey. Still other 

 very perfect specimens have been secured by the Yale Museum, 

 so that now ample material is available for investigating both 

 the present species and its near allies. 



On Plate VIII of this article is represented, one-eighth 

 natural size, a skull of Elotherium crassum, which is one of 

 the most perfect ever discovered. The lower jaws are in 

 place, and the nearly complete dentition is present and in fine 

 condition. Figure 1 shows this skull as seen from the left 

 side, with the jaws shut closely together, as found. One of 

 the most noticeable features is the long dependent process (m) 

 on the malar bone, which in this species extends downward to 

 the inferior margin of the lower jaw, in front of the angle. 

 This is the case when these processes are somewhat expanded 

 transversely, as shown in figures 2 and 3, which represent the 

 skull as it lay in the matrix. Another peculiar feature shown 

 in figure 1 is the series of processes on the lower jaw, the first 

 (a) being the dependent, everted angle of the ramus ; the sec- 

 ond (b) \ protuberance under the third lower premolar ; and 

 the third (c) a process below the base of the canine. These 

 processes are well shown, also, in figure 3. 



*This Journal, vol. v, p. 487, June, 187B. 



