OF THE WHITE RIVER BEDS OF MONTANA. 251 



cheek tooth — has two anterior grooves instead of one. It lops backward, its upper pos- 

 terior part resting against P 4 . On M 3 of the largest one (No. 42) there is a rudiment of 

 a posterior lobe. From Pipestone creek. 



Measurements. 



No. 43. No. 44. 



M. M, 



Length of molar-prernolar series 0123 .0141 



Lengl b of molar series ° 051 - 006 1 



Width of Mi °0°4 -0045 



Cylindrodon fontis, gen. et sp. nov. (Plate IX, Figs. 9, 9a.) 



Of this rodent I have two portions of right mandibular rami (Nos. 38 and 39). One 

 has all the cheek teeth and the greater part anterior to the ascending ramus; the other 

 has the three posterior teeth and part of the ascending ramus, but not the angle, coronoid 

 process or condyle. They were obtained from the Pipestone beds, associated with Palceo- 

 lagus, Ischyromis, etc. The Pipestone springs, near where the fossils were found, sug- 

 gested the specific name. 



The diastema was short; the teeth are cylindrical with a central enamel islet and 

 an_outer enamel inflection. The lower border of the ramus is convex fore-and-aft, and 

 is shallow but thick under M ¥ . The anterior angle of the masseteric area extends for- 

 ward to M T and is near the alveolar border. The anterior border of the ascending 

 ramus rises opposite My and leaves a broad space between the two. The surface of the 

 masseteric area is nearly flat, with a convexity considerably behind and above its ante- 

 rior angle. On the inside, back of the teeth, from the horizontal ramus a large con- 

 vexity passes backward, outward and upward on the ascending ramus. Above and below 

 this the bone is thin. The mental foramen is small and is situated above the middle of 

 the jaw, a little in advance of P T . 



The teeth are very characteristic, yet they are simple. As seen from above they 

 look like a larg-e comma, with a short tail directed outward. Their order of size, begin- 

 ning with the smallest, is M ¥ , I\, then M T and M ¥ , which are nearly equal in size. The 

 teeth are evidently quite long vertically, except the last which is short, as it is so nearly 

 approached by the posterior portion of the canine. The incisors are thicker antero- 

 posteriorly than transversely. 



Measurements. 



M. 



Length of molar premolar nones 



r. , . ,. , „ 0064 



Depth ol ramus under r ? 



Depth of ramus just back of My 004(l 



Thickness of ramus under Pj 



