Cope.] 45o [May 3, 1889. 



EXPLANATION OF PLATES. 

 Figiires of superior molar teeth of species of Hippotlieriura, natural size. 



Fig. 1. Eipjwtherium occidentale Leidy ; superior molar, from Cotton- 

 wood creek, Oregon ; internal view ; a, grinding face. 



Fig. 2. E. sinclairii Wortman; inner view ; a, grinding face. 



Fig. 3. n. rectidens Cope ; side view ; a, grinding face. 



Fig. 4. H. peninsulatum Cope ; side view ; a, grinding face. 



Fig. 5. E. speciosum Leidy ; including canine and incisor teeth. From 

 Kansas. 



Fig. 6. E. pUcatile Leidy ; grinding face ; from Leidy. 



Figs. 7-8. E. retrusum Cope ; first and second molars, grinding faces ; 

 a, posterior view of 7. From Kansas. 



Figs. 9-12. Superior molars doubtfully referred to E. retrusum or to 

 ProioJiippus or Eippidium profecium ; grinding faces. From 

 Kansas. 



Figs. 13-14. E. paniense Cope, from Colorado ; a, posterior view of 13. 



Fig. 15. E. calamarium Cope, from New Mexico ; from Cope in Report 

 Expl. Surv. W. of 100th Mer. ; G. M. Wheeler. 



Figs. 16-17. E. gratum Leidy, from Kansas ; a, anterior view of 16, 

 which is an m. iii, little worn. 17. a, posterior do. of 17, much 

 worn. 



Fig. 18. E. 'oenustum Leidy, from South Carolina ; grinding face ; a, in- 

 terior view. From Leidy. 



Figs. 19-20. E. relictum Cope, from Oregon ; a, anterior view of 19. 



Figs. 21-22. E. spJiOiodus Cope, from. Colorado. 22. Anterior premolar. 



Fig. 23. E. isonesum Cope, from Oregon ; including canine and incisor 

 teeth. 



Fig. 24. E. seversum Cope, from Oregon ; a, posterior side. 



Ifoie on Eippotherium rectidens. By E. D. Cope. 



In the preceding monograph of the genus Hippotherium, I have slated 

 that the //. rectideris Cope is probably founded on a tooth of the E. monte- 

 zurnce Leidy. A renewed examination of the type of the former convinces 

 me that I was premature in reaching this conclusion. Besides the straight- 

 ness of the crown, the E. rectidens possesses a peculiarity not shared by 

 any other species of the genus. The loop, or principal lobe of the lake 

 margins, belongs to the posterior lake, and not to the anterior lake. The 

 latter is its connection in E. montezumce, and in all other species of the 

 genus known to me. It is represented on Plate i, Fig. 3. 



