44 THE MERYCOIDODONTID/E 



Genus LIMNENETES Douglass 1901 

 Table 2 



Limnenetes platyceps Douglass 1901 

 Fig. 4; PL I, figs. 9-11 



Original Reference: Fossil Mammalia of the White River beds of Montana. Trans. Amer. Philos. 

 Soc. (2), XX, pp. 260-262, pi. IX, figs. 5-6. 



Type Locality: Thompson's Creek, on a side hill about three miles northwest of Three Forks, Gallatin 

 County, Montana. 



Geologic Horizon: Lower Oligocene (lower Chadron). 



Types: Genoholotype, Cat. No. 701 CM., skull of an old individual, with very much worn dentition. 

 Plesiotypes, Cat. No. 303 CM., part of upper jaw, with P 2 , P 4 , and M 1 ; Cat. No. 1086 CM., also part of 

 upper jaw of a young individual, with deciduous premolars and M 1 and M 2 ; and Cat. No. 1184 CM., part 

 of skeleton, including limb bones and pelvis. 



Specific and Generic Characters: The skull is mesocephalic, about the size of that of 

 Merycoidodon gracilis, and has an arched superior contour. The anterior zygomatic pillar expands 

 rapidly just in front of the orbits, and the arches extend backward in a nearly parallel manner, with 

 the greatest expansion at the middle of the zygomatic foramen. The arches are not heavy and rise 

 gradually aft to the highest point above the postglenoid processes. The nasal bones are relatively 

 narrow and flat, and are posteriorly truncated. The pars facialis of the lacrimal bone is moderately 

 large and is circular in outline, and it bears a shallow fossa in which the bone is rugose. The frontals 

 are wide, unreduced, slightly convex along the sagittal suture and slightly concave transversely on 

 either side of this convexity, becoming convex again as they approach the supraorbital margin. The 

 orbits are very large, circular in outline, and posteriorly open through a gape of 7 mm., and their 

 lacrimal border is rugose. They look mainly sidewise. The temporal ridges unite in a plane just 

 behind the anterior edge of the glenoid surface. The sagittal crest is very low and somewhat less 

 than a third of the skull length. The low supraoccipital crest slightly overhangs the occipital con- 

 dyles, and the wings are wide open. The interparietal bone is not coalesced with the parietals. 

 The brain case is moderately full and elongate and has a slight convexity along the parietosquamosal 

 suture. The external auditory meatus is small, and its direction is upward and slightly backward. 

 The basicranial axis is steep. The palate is narrow and somewhat concave transversely, while the 

 U-shaped palatonarial border lies between the anterior lobes of M 3 . The glenoid articular surface 

 has the same general proportions as that in Merycoidodon and is gently convex. The postglenoid 

 processes are moderately thin anteroposteriorly and wide transversely, and they bound almost the 

 entire posterior glenoid surface. The large bullae are transversely compressed and are proportion- 

 ally larger than those of Eforeodon. Index: 0.60. 



Foramina: The infraorbitals lie above the interval between P 3 and P 4 , or over the extreme 

 anterior edge of P 4 . The supraorbital foramina are 12 mm. apart and have a channel from each 

 running forward and slightly inward, then outward, and finally downward and backward to the 

 infraorbital foramen. The foramen ovale occupies its normal position, while the small foramen 

 rotundum lies just outside the posterior end of the pterygoids. The posterior palatine foramina are 

 opposite the interval between P 4 and M 1 . 



Dentition: Teeth brachyodont and specialized. M 1 wider than long, M 2 nearly square, and 

 M 3 slightly longer than wide. The faces of the metacones and paracones are nearly in the same 

 plane and do not appear to be offset, as they are in Merycoidodon. P 4 is much wider than long 

 and has no pit in the anteroexternal portion. P 3 is subtriangular, the anterior part having but a tiny 

 anterointernal crescent and no anterointermediate crest. P 2 is similar in construction to P 3 but is 

 smaller. The premolar series is incomplete, but it appears to have been proportionally smaller than 

 in Merycoidodon. 



