238 the merycoidodontim: 



I believe that these are all adolescent characters of a robust male of L. decora. Perhaps the 

 specimen may be a male of L. minora, and were it not for the later geologic age, I should consider 

 the latter species as referable to L. decora. Both L. decora and L. minora are of nearly the same 

 size. This Yale specimen and the latter species are of lower Miocene age, while the former is upper 

 Oligocene. Both the Miocene forms, I think, are direct derivatives of L. decora and are so close to it 

 that my feeling is rather that L. decora continues on into the Miocene than that we have sufficient 

 changes to warrant a new species. 



Leptauchenia major Leidy 1856 

 PI. XXXVI, figs. 5-6; PL XXXVII, figs. 6-8 



Original Reference: Notice of some remains of extinct vertebrated animals. Proc. Acad. Nat. Sci. 

 Phila., VIII, pp. 163-164. 



Type Locality: White River Valley, South Dakota. 



Geologic Horizon: Upper Oligocene (upper Brule). 



Types: Cotypes, Cat. Nos. 10871-74, 1 0941-42 A.N.S.P., parts of upper and lower jaws, with teeth and 

 with a badly damaged skull. Plesiotype, Cat. No. 10118 Y.P.M., moderately well-preserved skull with jaws. 



Specific Characters: The skull of the largest species in this genus is intermediate in size 

 between that of M. culbertsonii and M. gracilis. The malar below the orbit is decidedly deep, the 

 squamosal part of the zygomata is light, and the maximum expansion is just posterior to the orbits. 

 The zygomata slope gently upward and backward. The facial vacuities are large and extend poste- 

 riorly nearly to a line through the middle of the orbits. The nasal bones are very narrow, termi- 

 nating posteriorly in points close to the antorbital margin. For a short distance anteriorly the nasals 

 unite with the maxillaries, then broaden out at this point and extend to a line above the incisors. The 

 muzzle shows a steep forward declivity in superior contour and is marked by a prominent ridge from 

 the infraorbital arch to the anterior portion of the nasals. The facial extent of the lacrimal is small, 

 and the bone has a small, shallow fossa. The frontals are narrow transversely, while, as a result of 

 the great invasion of the facial vacuities, they are very much reduced anteroposteriorly. These 

 bones are slightly elevated along the sagittal suture and are somewhat depressed between the central 

 ridge and the supraorbital margins. The orbits are relatively smaller than in L. decora and are 

 situated slightly lower vertically. The temporal ridges unite at the postorbital constriction to form 

 a rather long, but low, sagittal crest. The supraoccipital crest does not overhang the occipital con- 

 dyles, and the wings are transverse. The brain case is less flat than in L. decora and is well expanded 

 laterally. The external auditory meatus is directed backward and upward. The palate is nearly flat, 

 with the palatonarial border opposite M 3 . The basicranial axis is not steeply inclined. The glenoid 

 surface is normal, and the postglenoid process is small, so that the condyle of the lower jaw seems 

 nearly to touch the paroccipital process. This process is plate-like transversely and narrow antero- 

 posteriorly; inferiorly it diminishes rapidly to a point slightly below the lowest part of the bulla. 

 The bullae are very much inflated, extend somewhat forward of the glenoid articular surfaces, and are 

 roughly triangular rather than oval in outline, with the bases posteriorly located. Index: 0.71. 



Mandible: The symphysis makes an angle of 45° with the tooth row. It is concave vertically 

 and convex transversely, without an appreciable tubercle at its inferior termination. The horizontal 

 ramus is robust and of nearly uniform depth beneath the tooth row, and the angle of the ramus barely 

 descends below the line of the inferior margin. The ascending ramus is wide and relatively deep. 

 The shallow masseteric fossa is not extensive, while the coronoid process is short and thin. The 

 condyle is small and of normal shape, with the sigmoid notch wide open. 



Foramina: The infraorbitals lie above the posterior part of P 3 , and the supraorbitals lie almost 

 exactly between the mid-line of the frontals and the supraorbital margins. 



Dentition: The molars are characterized by very heavy parastyles and mesostyles, relatively 

 heavier than in any other species of Leptauchenia and also heavier than in Merychyus. The pre- 

 molars are less crowded than in L. decora, and the relative increase in size from M 1 to M 3 is greater. 



