186 TEN years' progress in vertebrate paleontology 



which are on record comparatively few are known from the complete 

 skull or skeleton, most of them only from parts of the jaws. The most 

 important additions of the last decade are : 



1. Complete skeletons and series of skulls of several Eocene Eodentia 

 of North America. 



2. Skeletons and skulls of the principal Miocene rodents of South 

 America. 



3. Skulls and skeletons of Steneofibei- and Mylagauhis from the North 

 American Miocene and Pliocene. 



4. Skulls of various Oligocene rodents from North America and re- 

 mains of rodents from the Fayum fauna in Egypt. 



PRINCIPAL CONCLUSIONS FROM THE STUDY OF THE MATERIAL 



1. The Lagomorpha have very little, if anything, to do with the re- 

 maining rodents. They have changed but little since the Oligocene, and 

 their earlier history is totally unknown. 



2. The Simplicidentate rodents are a natural group derived from the 

 Eocene Ischyromyidse. 



3. The Tillodontia have nothing to do with the Eodentia. but are 

 probably related to the early Insectivora. The same is true of the 

 Proglires. Palaeontology throws no light on the derivation of the Eocene 

 Eodentia or their affinities to other orders. 



4. The Miocene rodents of South America are all Hystricomorpha. 

 The Theridomyidse of the early Tertiary of Europe appear to be transi- 

 tional from IschyromyidaB to Hystricomorpha, but their relations to the 

 Miocene Hystricomorphs of South America are not yet clear. 



5. Castoroides is a Sciuromorph related to the true beavers. Its 

 Chinchilla resemblances are wholly due to parallelism. Amblyrhiza, on 

 the other hand, is probably related to the Chinchillas. 



6. Dcemonelix is not a fossil plant ; most of the forms attributed to it 

 are probably fossilized burrows of some rodent, presumably Steneofiber. 



MOST IMPORTANT INVESTIGATIONS DESIRABLE IN THIS LINE 



1. The origin and affinities of the Duplicidentata. 



2. A thorough monographing of the Eocene and Oligocene rodents 

 and the light they throw on the origin and relationships of the Simplici- 

 dentate families. 



3. Eeinvestigation of the Theridomyidae in their relations to the Santa 

 Cruz and other South American Hystricomorphs; and if they are ances- 

 tors of the latter, a satisfactory explanation of their migration. 



