18S9 ] 4:60 [Cope. 



aa. Anterior internal column joining the posterior internal 

 column. 

 Grinding face oblong, 20 by 17 mm. ; lakes rather complex, with a large 



loop H. retrusum. 



AAA. Section of anterior internal column round. 

 Larger; grinding face square, 19 by 20 mm. ; complexity medium ; pos- 

 terior column not so prominent inwards H. paniense. 



Smaller ; grinding face longitudinal, 19 by 17 mm. ; lakes complex ; pos- 

 terior internal column not prominent U. vemistum. 



Smaller ; grinding face transverse, 16 by 19 mm. ; posterior inner column 



nearly as prominent as anterior innei' H. relictum. 



II. Posterior internal column as prominent inwards and of nearly equal 

 size with the anterior, and nearly cut off from the posterior inner 

 crescent. Anterior inner column with an apex directed towards the 

 anterior inner crescent. Siylonus Cope. 

 Large ; grinding face 24 by 23 mm. ; largest premolar short, wide 



H. calamnrium. 

 Smaller ; grinding face 20 by 18 mm. ; largest premolar elongate, wedge- 

 shaped H. isonesum. 



Smallest ; grinding face 17 by 17 mm. ; lake borders simple. .11. seversum. 

 The stratigraphic position of these species is as follows : 



Lower Pliocene. 



H. relictum Cope. 

 ? H. venustum Leidy. 

 Ticholeptus bed. 



H. seversum Cope. 



H. isonesum Cope. 

 Loup Fork (Upper Miocene). 



H. calamarium Cope. 



H. paniense Cope. 



H. retrusum Cope. 



n. gratum Leidy. 



H. sphenodus Cope. 



H. plieatile Leidy (? horizon). 



H. speciosum Leidy. 



S. sindairii Wortman (? horizon). 



H. peninsulatum Cope. 



H. montezumce Leidy. 



H. oceidentale Leidy. 



Of the preceding fourteen species I have seen teeth of all but the H. vemis- 

 tum of Leidy, which was found in the South Carolina phosphate beds. I 

 have parts of several individuals of the H. gratum from Kansas, and the H. 

 retrusum is from the same locality. H. plieatile is from Florida, and the 

 JI. peninsulatum and H. montezumce are from Eastern Mexico. I have 



PROC AMER. PHILOS. SOC. XXVI. 130. 3C. PRINTED JUNE 1, 1889. 



