EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHEEES 



373 



although nearer the former in shape and much larger 

 than in the latter. The anteroposterior and trans- 

 verse dimensions of the incisors are, i', 18 by 14 

 millimeters; i^, 19 by 17; i^ 22 by 20. The incisors 

 in general resemble those of M. manteoceras in their 

 rounded front faces and obtusely pointed tips but 

 differ in the form of the posterior cingulum, which is 

 now represented by a very large, obtuse basal rim. 

 The posterior face of i', i^ shows a median vertical 

 ridge. The posterior face of the large i' is much worn. 

 The canine is very stout, with widely protruding and 

 divergent fangs; crown measurements (ap. by tr.), 

 27 by 20 milhmeters ; it is followed by a large post- 

 canine diastema (26 mm.), which distinguishes 

 this species from M. manteoceras, and also by a 

 marked postcanine constriction. 



Premolars. — P' (ap. 22 mm., tr. 11) seems to 

 be a somewhat more compressed, elongate tooth 

 than in the preceding species, in which the pos- 

 terobasal cingulum is produced upward along the 

 median line into a very low incipient cusp. In 

 p^ (25 by 21) the deuterocone is still confined to 

 the postero-internal corner of the tooth but is a 

 little more advanced than in M. manteoceras; the 

 tritocone is also slightly more developed but not ^ 

 so much as in either StJienodectes incisivus or Doli- 

 chorMnus. The external cingulum opposite the 

 tritocone is rounded. In p^ (24 by 29) the deutero- 

 cone has a rather backward appearance as com- 

 pared with the same cusp in M. washakiensis, but 

 the internal cingulum is pronounced, although still 

 incomplete opposite the middle of the deutero- 

 cone; the protocone is still much larger than the 

 tritocone; the "parastyle" is pronoupced; the ecto- 

 loph convexities are marked; the external cingulum 

 is pronounced except where it "festoons " the proto- 

 cone convexity. In p^ (28 by 33) the deuterocone 

 seems less robust than in M. wasJialciensis; the cin- 

 gulum is robust but does not surround the deu- 

 terocone; the "parastyle" is prominent, and the 

 protocone convexity broad at the base; the trito- 

 cone is at least no bigger than in M. wasJialciensis; the 

 external cingulum is a broad, rounded ridge opposite 

 the tritocone. 



Molars. — The molars (m^-m^, 138 mm.) are some- 

 what larger than those of M. wasJialciensis but other- 

 wise agree fairly well. The external cingulum is very 

 pronounced opposite the valleys. The molars show a 

 marked asymmetry of the external V's, the anterior 

 V being more widely open and the posterior having a 

 short posterior limb. The antero-internal cingula are 

 heavy but not complete around the inner sides of thepro- 

 tocones (contrast M. wasJialciensis). In m^ the postero- 

 internal corner is less angulate than in M. wasJiaJciensis. 

 The anteroposterior and transverse dimensions are, 

 m\ 37 by 38 millimeters; m^ 48 by 48; m', 48 by 52. 



Other measurements of M. uintensis are given in the 

 table above. 



Manteoceras uintensis? 



From the base of Uinta C in 1895 Peterson obtained 

 a very large skull, apparently female (Am. Mus. 2029), 

 which unfortunately is too aged as well as. too much 

 crushed and imperfect to afford distinctive characters 

 for definition. It is somewhat smaller than the type of 

 M. uintensis. If more complete it might be found to 



Figure 312. — Type skull of Manteoceras uintensis 



One-fourth natural size. Carnegie Mus. 2388. "About 5 miles northeast of well 2, 

 Uinta Basin; from gray sandstone in red Uinta beds, lower portion of horizon C." 

 Ai, Side view, nasal region crushed; A2, palatal view, crushed laterally. 



represent a female of M. uintensis (with which it 

 agrees in the retarded evolution of the premolars) or a 

 species transitional between Manteoceras wasJiaJciensis 

 and a higher stage of evolution. Size or metatrophic 

 characters are truly progressive and undoubtedly 

 correlated with other characters of distinct specific 

 value. Its total length, condyles to incisive border, 

 is about 555 millimeters, as compared with 523 in the 

 largest skull of M. manteoceras found in Bridger D. 

 The grinding teeth, p^-m^, measure 227 millimeters, 

 as compared with 203 in the largest of the specimens 

 of M. manteoceras from Bridger D and 240 in M. 

 uintensis. Its progressive zygomatic brachycephaly 

 is indicated by the widely arching zygomata, which 

 attain a transverse width of about 360 millimeters. 



