FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 129 



anterior to P^ The enlarged teeth are thus not rigidly proved to be 

 the same, and with his customary caution Matthew stressed the fact 

 that they might not be homologous. The premolars are different in 

 the two groups, although I believe that the difference has been over- 

 emphasized. In the "Microsyopinae" P*4 are less elevated and more 

 molariform than in the "Mixodectinae." The molars are almost 

 identical in the two groups, except that in the earlier forms there is a 

 distinct and markedly internal hypocone, while in the later the 

 hypocone is anomalously small and is less internal. 



The two genera discovered since Matthew's work, especially 

 Eudaemonema, alter this situation. Eudaemonema has the anterior 

 (lower) dentition less specialized than in Mixodedes, and Elpidophorus 

 has it either closely similar to Alixodedes or slightly less reduced. In 

 both cases there is no reason to beUeve that the enlarged incisor is 

 not homologous with that of Mixodedes and also with that of Cyno- 

 dontomys. In both genera P4 is submolariform. In Eudaemonema 

 it is very similar to that of Cynodontomys and Microsyops, rather than 

 to the contemporary Mixodedes. In Elpidophorus it is aberrant in 

 having a strong, projecting paraconid. P* is not known in Eudae- 

 monema; in Elpidophorus it closely resembles that of the Eocene 

 genera. In Eudaemonema the upper molars have strong, internal 

 hypocone, comparable to Mixodedes, while Elpidophorus is more 

 like the Eocene genera in this respect. These genera thus mingle 

 characters of the "Mixodectinae" and the "Microsyopinae", and 

 they make it impossible to maintain a consistent separation between 

 these groups. At the same time they strongly support the reahty of 

 a relationship between them. 



For one reason or another the known Paleocene genera of this 

 family cannot be considered ancestral to each other or to the Eocene 

 forms. Thus Eudaemonema is the most primitive as regards the 

 retention of anterior teeth, but its premolars are more advanced than 

 in Mixodedes and Indrodon, and its strong, projecting hypocones seem 

 to exclude it from the ancestry of Elpidophorus or of Cynodontomys 

 and Microsyops. Mixodedes and Indrodon cannot be ancestral to the 

 later forms for the same reason and cannot be structurally ancestral 

 to the contemporary Eudaemonema because of their reduced anterior 

 dentition. Elpidophorus has aberrant specializations in P4 and in 

 details of molar structure that seem to exclude it from consideration 

 as the ancestor of the Eocene genera. Evidently four different groups, 

 intimately related but all on different lines of phyletic descent, are 

 represented. These can be contrasted, among other details, by the 

 characters listed in table 28. 



