68 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



MENISCOTHERIUM ROBUSTDM Thorpe 

 (Plate 10, figures i and 2) 



The distribution of Meniscotherium rohustum would appear to 

 be characteristic of the upper part of the Knight formation beneath 

 the Tipton tongue and to be nearly limited to the Green River Basin 

 of Wyoming. Its area of greatest abundance is the vicinity of La 

 Barge and Big Piney, but it has been found near Tipton Butte, and 

 to the southeast of the Rock Springs uplift as well as on its western 

 flank. Also, a maxilla and a portion of a lower jaw, which may repre- 

 sent this species or a form near it, were found in the adjacent Fossil 

 Basin at localities high in the Knight beneath the Green River beds 

 on Fossil Butte. Besides these, maxillae and a jaw portion belonging 

 together were discovered in association with a considerable amount 

 of Corypliodon material on the escarpment to the west of Elk Moun- 

 tain. Distribution of the species, however, does not appear to have 

 extended as far east as the Muddy Creek area on the east side of the 

 Washakie Basin. No material of Meniscotherium has been observed 

 in any of the several collections from beds beneath the Tipton tongue 

 in the vicinity of Dad and Baggs, Wyo., and this species has not been 

 reported from either the Wind River or Bighorn Basins. 



While the vertical range of Meniscotherium rohustum is limited 

 upward, as far as known, by the Fontenelle or Tipton tongue of the 

 Green River, its distribution downward remains somewhat uncertain. 

 It may well characterize only the Lostcabinian level but if it evolved 

 in situ from the early GraybuUian M., cf. priscum, of the area, the 

 Lysitean stage of this development has not been clearly demonstrated 

 in the Green River Basin. It is entirely possible that the Fossil Butte 

 specimens which seem near M. rohustum represent this age. The 

 teeth in the maxilla (U.S.N.M. No. 22670) are larger than in the 

 New Fork M., cf. chamense, but are at about the lower limit of the 

 observed range in size for M. rohustum. Only two maxillae in the 

 La Barge collection have teeth as small. The lower jaw fragment 

 (U.S.N.M. No. 22794) has Pg and P4 only slightly larger than in the 

 M., cf. chamense, material but the jaw itself is about as robust as in 

 M. rohustum. It is interesting to note, however, that the specimen 

 from the Fossil Basin locality west of Efc Mountain (U.S.N.M. No. 

 22795), evidently a Gray Bull level, has teeth fully as large as in 

 M. rohustum. There is no association here with M. priscum, however. 

 Presumably the horizon is not as early as that at Bitter Creek. 



