1900.] O shorn, Phylogeny of the Rhinoceroses of Europe. 233 



on the nasals, beginning in the Middle and Upper Oligocene stages. 3. Lower 

 canines sub-triangular in section, flattened on outer and upper sides, slightly 

 convex on lower side (as observed in Middle and Upper Oligocene American and 

 European types). 4. First lower premolar early reduced or wanting, as ob- 

 served in European and American types (also in R. gaudryi and R. velatimim). 

 5. Molars quadrate, frequently exhibiting a conical cingule or cusp at the open- 

 ing of the median valley. 6. Narrow skull, with narrow elevated occiput, ex- 

 panding and notched above. Zygomatic arches suddenly expanding posteriorly. 



These are some of the characteristic features which are ob- 

 served in both European and American types and reach their 

 full development in the Upper Oligocene. The nomenclature is 



Fig. 2. Ronzotheriunt gaudryi. Type: Paris. A^ Internal view of left ramus. <4*, 

 External view. A °, Superior view. X |. 



still uncertain ; to the Lower Oligocene forms, which probably 

 possessed upper canine teeth, the generic name Ronzotherium 

 Aymard possibly applies. It is possible that the type species, 

 R. velaunum^ belongs to the Amynodontidse, in which case it may 

 anticipate the genus Amynodon Marsh. If, however, it belongs to 

 the Diceratheriinse it may anticipate the genus CcEtwpus Cope 

 (primitive hornless Rhinoceroses with precociously tridactyl feet), 

 or the genus Leptaceratherium Osborn, or TrigQuias Lucas (primi- 

 tive hornless Rhinoceroses with persistent upper canine teeth). 

 To the Upper Oligocene form, Diceratheriwn Marsh is applicable. 



