60 



rather thorough coossification of the two rami. The hinder end of the symphysis is m Una 

 with the front root of the third premolar. Two mental foramina are present, the larger of 

 the two beneath the anterior root of the third premolar,, the other beneath a point slightly in 

 advance of the second premolar. 



Length of premolar series 

 Length of alveolar space of 



Measurements. 



MM. 



QQ 



Length of specimen ° 



1st premolar * 



2nd " ■ 11 



3rd " 15 '5 



4th " 16 



1st molar 1 1 



Antero-posterior diameter of alveolus of canine 10 



Transverse diameter of same, approx ' 



Space between alveoli of canine and 1st premolar 3 ^ 



" " " 1st and 2nd premolar 3 ■ 5 



Depth of ramus at point between 4th premolar and 1st molar 34 



Depth of ramus at mid-height beneath same point 12 



Thickness of ramus at posterior end of symphysis 16 



Collector T. C. Weston. Headwaters of Swift-current creek (Bone coulee), Cypress hills, 1888. 



A left lower tooth, found separately in 1904, plate YII, %. 3, has the proportions of the 

 second premolar of Hycenodon. The alveoli (containing roots) of the second premolar of the 

 left ramus, mentioned above and referred to H. cruenius, indicate by their size that this separate 

 tooth is probably referable to this species. 



Ht^nodon crucians ? Leidy. 

 Plate VII, figs. 4, 5 and 6. 



Hymnodon crucians, Leidy, 1853. Proc. Acad. Nat. Sci. Phila., vol. VI, p. 393. 



A second species o^ Hyanodon is represented by a superior left fourth premolar (collec- 

 tion of 1904). The tooth is not quite as large as the corresponding premolar oi H. crucians, 

 as described and figured by Leidy in 1869 in "The Extinct Mammalian Fauna of Dakota and 

 Nebraska"*, but approaches closely to it in shape ; it is referred to this species provisionally. 



In the Cypress Hills tooth the protocone is large and compressed, thetritocone (posterior 

 cusp) is small and slightly trenchant, the deuterocone (interior cusp) is fairly developed on 

 the inner side in line with the protocone. There is an inconspicuons protostyle (anterior 

 basal cusp ) and exteriorly, at the mid-length of the crown, the basal cingulum is feebly 

 developed. 



Measurements. 



MM. 

 Max. height of crown of tooth 8 *> 



" length" " " '..'.'.'.'.".'.'.'.'.'.'.'.'"...'.'. ' 1016 



" breadth " " " ' ' ' 7.3 



The specimen represents a species of about the same size as H. crucians, Leidy, but 

 possibly distinct. 



369, 



I. pril."""""' '»*™""^«'^° f*™^ of I>akota and Nebraska. Jour. Acad. Nat. Sci. Phila., second series, vol. VII, pp. 48 and 



