SINCLAIR— A NEW IIOPLOPHONEUS. 



97 



HOPLOPHONEUS MENTALIS Sp. IIOV. 



Type No. 12515, Princeton University Geological Museum, col- 

 lecting locality 1015A1, left ramus of the lower jaw with the canine 

 and third and fourth premolars in place (Fig. i), secured by the 

 1920 South Dakota expedition from the uppermost levels of the 

 Titanotherium beds (Chadron formation), two to two and one half 

 feet below the thin local bed of white limestone at the contact be- 

 tween the Chadron and Brule formations (Oreodon beds), and two 

 and a half to three feet above titanothere bones in place, in the 

 valley of Indian Creek, near Taylor's ranch, west of Hart Table in 

 Pennington County (locality shown in Fig. 2 of Plate i of the pre- 

 ceding paper, in about the center of the picture). 



MEASUREMENTS. 



H. occi- 

 dentalism 



H. men- 



talis. 



No. 



12515- 



H. inso- 



lens, 



No. 



11372.2 



H. robus- 



tus, 



No. 



10647.2 



Depth of chin at flange 



" " ramus at P3_. 



"ml , 



Length of ramus 



Height at coronoid 



Width of lower canine at base of crown . 

 Length p3 



P4; 



mi 



Diastema c-p3 



Anterior margin of masseteric fossa to 

 canine ridge, length 



80 mm. 

 32 

 31 

 164 

 50 

 13 

 12 

 17 

 22 

 42 



67 mm. 



25-5 

 26.5 



145 

 43 



6 



6.5 

 12.75 

 17-5 

 33 



80 



52 mm. 

 26 

 26 

 138 



6 



8 

 14 

 14-5 

 33 



79 



54 mm. 

 26 

 26 

 134-5 

 39 

 6 



6.5 

 13-5 

 16.5 

 30-5 



74-5 



So far as I am aware, this is the first Hoplophoneus to be de- 

 scribed from the Titanotherium beds and is strikingly differentiated 

 from all of the species of the overlying Oreodon beds by the extraor- 

 dinary depth of the chin (as suggested in the specific name pro- 

 posed), a character reminiscent of the great development of this 

 structure in Hatcher's Eusinilus dakotcitsis from the Protoceras 

 beds, to which the new form seems to be transitional. 



^Williston's measurements, Kansas Univ. Quarterly, Vol. IIL, No. 3, p. 72, 



1895. 



2 Specimens in the Princeton Geological Museum used by G. L Adams, in de- 

 fining these species. 



