328 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



matJierium uitimum. The post-tympanic processes 

 are broadly oval, and the paroccipital processes are 

 more slender and acute than in T. uitimum. A dis- 

 tinctive feature is the relatively sharp ridge con- 

 stituting the inferior border of the malars from the 

 point where the arch leaves the skull to their junction 

 with the squamosals. The occipital view of the skull 



fu o (J^ ^car.ex.) 



Figure 277. — Type skull of Palaeosyo'ps leidyi 

 Top view. One-fourth natural size. Am. Mus. 1544 (type) . Henrys Fork 

 Bridger Basin, Wyo.; Bridger formation, level probably upper C or D. 



reveals a large mastoid foramen. This is also observed 

 in LimnoJiyops laticeps and appears to be a distinctive 

 feature of this series of crania. Unlike that of L. 

 laticeps (figs. 261, 264) the summit of the occiput is 

 not defined by a crest but passes directly into the 

 vertex. 



In the lateral view, in addition to the features 

 already mentioned, attention should be called (1) to 

 the prominent antorbital knob or process on the 

 lacrimals, to the abbreviation of the face, the space 

 between the orbit and narial notch measuring but 

 70 millimeters; (2) to the absence of any horn rudi- 

 ment; (3) to the convexity of the maxillaries as seen 

 in side view; (4) to the abbreviation of the premaxil- 

 laries; (5) to the semicircular section of the malars 

 below the orbits, which passes into the deep and later- 

 ally compressed section, with the inferior masseteric 

 ridge beneath and behind the postorbital processes. 

 The anterior and superior views of the cranium (figs. 

 277, 279) illustrate the characteristic rounded pre- 



maxillary symphysis and the abbreviation of these 

 elements and the correlated rounding and depression 

 of the maxillaries below the narial notch. 



Type lower j aw : The perfectly preserved j aw of this 

 specimen (fig. 280, C) exhibits the massive chin of the 

 male form. On the lower surface we see the short 

 (24 mm.) digastric fossa, the massive thickening of the 

 mandibular rami (35 mm.), now extending back 

 below m2, the curvature of the lower border of the 

 ramus, the increased depth (98 mm.) behind m^, the 

 triangular form of the free portion of the coronoid 

 process, the broadly transverse expansion of the base 

 of the coronoid process behind nis, the transverse 

 extension (74 mm.) of the condyles, the great elevation 

 (175 mm.) of the condyles above the bottom of the 

 angle, the extension of the angle backward to a less 

 degree than in Manteoceras, also on the outer surface 

 the subdivision of the masseteric fossa by a horizontal 



xictr 

 \ -ms.per 



Figure 278. — Type skull of Palaeosyops leidyi 



Palatal view. One-fourth natural size. Am. Mus. 1544 (type). Henrys 

 Fork, Bridger Basin, Wyo.; Bridger formation, level probably upper C or D. 



ridge extending forward and downward from the 

 condyle. 



Dentition of the type: Diastemata appear between 

 the opposite incisor series and behind both the incisors 

 and the canines. P* is too much worn to show 

 the mesostyle. On the molars the conules are almost 

 completely worn ofi'. External cingula are well 

 marked, especially on m'. In the lower jaw the 



