LIMNENETF.S, MERYCOIDODON 45 



Skeleton: The limb bones are slender and long, after the manner of Merychyus. The humerus 

 has a deep epicondylar pit, a very high great trochanter, and a prominent lesser trochanter, and it 

 is more nearly straight than the usual merycoidodont form. The ulna has a very long olecranon 

 process, while the radius is flattened, though not to so great a degree as in some of the later species. 

 The pelvis is moderately short and is widely expanded posteriorly. The femur has expanded 

 terminals, while the cnemial crest of the tibia is prominent but short. The elongated foot is some- 

 what like that of Merychyus, with long, slender toes and narrow unguals. 



Discussion: Douglass considered the dentition to be very close to that of Merycoidodon. 

 Superficially it does appear so, but in detail it can be seen that these teeth are more specialized than 

 those of that genus or of Eporeodon. I believe that Douglass was correct in assigning Limnenetes to 

 the Eporeodon group, on the basis of the large bullae and other similarities of skull structure. 

 Loomis (1924A and B) corroborated the opinion of Douglass and suggested that this genus might 

 have initiated the Eporeodon-Mesoreodon-Promerycochcerus-Merycochcerus-Pronomotherium line. 

 The specialized tooth structure of Limnenetes seems to indicate, however, that this genus does not 

 stand in the main phyletic line and therefore is not directly ancestral to Eporeodon. The latter 

 has a pit in the anteroexternal corner of P 4 , and P 3 possesses the anterointermediate crest and anterior 

 crescent, thus making them unlike these two teeth of Lhnnenetes. 



Hay placed this genus, as well as Oreonetes, under the Dichobunidae. I fail to understand his 

 reason and believe them to be true merycoidodonts, with the characters which we might expect to 

 find in members of this family in the lower Oligocene. 



Etymology: Limnenetes (marsh + injected = subjected to marsh life). 



Genus MERYCOIDODON Leidy 1848 

 Table 2 



Original Reference: On a new fossil genus and species of ruminantoid Pachydermia: Merycoidodon 

 Culbertsonii. Proc. Acad. Nat. Sci. Phila., IV, pp. 47-50, figs. 1-5. 



Synonyms: Oreodon Leidy, 1851; Cotylops Leidy, 1851. 



Genotype: M. culbertsonii Leidy. 



Genocotypes: Cat. Nos. 10727 and 10728 A.N.S.P., fragment of maxillary and portion of right ramus, 

 both with teeth. 



Distinguishing Characters: Skull mesocephalic (average index 0.57), ranging in length 

 from 120 mm. to 220 mm.; nasal bones long and medium in width; premaxillaries not coossified; 

 muzzle narrow and face approximately equal to half of skull length; antorbital fossa shallow to 

 deep; orbits medium-sized; frontals wide and unreduced; brain case narrow and elongate; sagittal 

 crest not especially high and supraoccipital crest moderately produced; zygomatic arches much 

 lighter in squamous portion when compared with malar part; bulla? very small to medium; 

 mandible posteriorly wide, coronoid low, and masseteric fossa descending below level of alveolar 

 parapet. 



Dentition: Brachyodont. Superior premolars moderately broad, with anterior part not 

 particularly well developed; P 4 having an anteroexternal pit, shown in unworn teeth; anterior 

 three premolars having an anterointermediate crest dividing the anterior basin. Inferior premolars 

 lacking anterointermediate crest and weak posterointermediate crest taking off from median crest 

 instead of from primary cusp as the more normal condition. 



Skeleton: Limbs of moderate length, with vestigial pollex in manus. Size varying from 

 690 mm. in length and 320 mm. in height (M. gracilis) to about 1000 mm. by 420 mm. (M. cul- 

 bertsonii) in the same dimensions. 



Discussion: The type of this genus was the first specimen collected and described of this whole 

 great division of the Mammalia. 



