246 THE merycoidodontid;e 



There is a very interesting skull with jaws, Cat. No. 1-28-8-31 N.S.M., which in many ways 

 partakes of the characters of both C. densus and C. lullianus, although it is nearer to the former and 

 for the present identified with that species. The specimen was collected 200 yards west of Reding- 

 ton, Morrill County, Nebraska, in the lower Miocene Gering formation. It is a robust, heavy skull, 

 with an appreciable amount of rugosity developed in various bones. The teeth are wide and heavy. 

 M 1 has an index of 1.66, that is, the tooth is the widest in proportion to length of any so far 

 described. In the type of C. densus it is only 0.81 and in C. lullianus 1.14. The face is short (index 

 0.306), as in C. densus (index 0.284), while it is longer in C. lullianus (index 0.391). The dental 

 index in the three above-mentioned specimens is 0.70, 0.60, and 0.69 respectively, that is, the molar 

 length is slightly shorter and the premolar slightly longer than in C. densus, while the proportions 

 are nearly the same as in C. lullianus. The skull index is nearly the same in all three, 0.732 for this 

 specimen, 0.717 for C. lullianus, and 0.72 for C. densus. 



The Nebraska specimen is moderately old, and the teeth are fairly well worn, which may 

 explain the greater width of M 1 , the rugosity of the skull bones, and the slightly greater degree of 

 brachycephaly. However, I am of the opinion that this represents a male and, furthermore, that the 

 species with narrow teeth are probably females. Other distinctions between this specimen and the 

 type of C. densus are of minor importance and can be due entirely to sex or to individual variation, 

 as, for instance, the palatonarial border being a little further forward and the canines slightly more 

 robust. On the whole, this specimen fits all the conditions which we should expect to find in the 

 male of C. densus, provided, of course, that the type is a female, which I think is quite likely. 



The two skeletons, shown on PI. XLIX, were also collected in the Gering formation in Morrill 

 County, and probably should be referred to this species. 



Cyclopidius lullianus Thorpe 1921 

 Figs. 173-177 



Original Reference: Leptauchenia Leidy and Cyclopidius (Pithccistes) Cope. Amer. Jour. Sci. (5), 

 I, pp. 413-415, figs. 1-3. 



Type Locality: Muddy Creek (Spanish Mines), Wyoming. 



Geologic Horizon: Lower Miocene (lower Rosebud). 



Type: Holotype, Cat. No. 10117 Y.P.M., skull, lacking left zygoma and part of cranial region; and 

 jaws, of which upper part of left ascending ramus is missing. Collected in 1908 by Professor R. S. Lull, for 

 whom the species is named. 



Specific Characters: This is the largest known species of the genus, the skull length being 

 approximately that of a small Merycoidodon culbertsonii. The muzzle is short, and the zygomata 

 are much expanded, their greatest transverse diameter being just in front of the glenoid surface. 

 The malar is exceedingly thick and deep, with an inferoposterior process extending almost to the 

 glenoid surface, while the squamosal part of the zygoma is weak and trends rather abruptly upward 

 posteriorly. The facial vacuities are very large, extending posteriorly into the frontals as far as a 

 line through the middle of the orbits and anteriorly to a point above the front of P 2 . Thus the 

 frontal, nasal, maxillary, and probably the lacrimal bones have all been reduced to form this vacuity, 

 which is the largest known in the family. The nasals are narrow strips of bone, expanding at the 

 sutural contact with the maxillaries, beyond which point they are produced but a very short distance. 

 They do not make contact with the premaxillaries, which likewise are very much reduced in size and 

 lie below and partly on the sides of the anterior nares. Posteriorly the nasals terminate in points. 

 The lacrimal is of small extent facially and bears a shallow fossa. The frontals are very much 

 reduced and are narrow anteroposteriorly. A rather shallow but well-marked depression separates 

 the sagittal ridge from the slightly elevated supraorbital borders. The orbits are closed, the post- 



