THE INSECTIVORA 659 



for, with a single somewhat doubtful exception, the entire order of Insec- 

 tivora is absent from the Tertiary faunas of South America, while they 

 were many and varied in North America, especially in the okler Tertiary. 

 The two Antillean insectivores are not nearly related to each other, nor 

 to any other genera of the order; they are placed in families by them- 

 selves. It has been repeatedly stated that Solenodon is related to the 

 Malagasy Centetidae, but in fact the affinity is a very distant one. Neso- 

 phontes is equally peculiar, and while it has some affinities with the 

 Soricoidea (moles and shrews), they are very distant. Tlie nearest rela- 

 tives of both — collateral ancestors, perhaps — are certain imperfectly 

 known insectivores of very primitive type in the North American Eocene 

 and Oligocene. 



THE RODENTIA 



The rodents are clearly of South American affinities. Tliey are all 

 liystricomorplis — a group chiefly South American since the middle '^i'er- 

 tiary (if not before). The only North American hystricomorph is the 

 porcupine. Pleistocene and Eecent, and whose ancestors have been recog- 

 nized in the South American Tertiary. No traces of the hystricomorph s 

 have been discovered in the Tertiary of North America.^ There are cer- 

 tain Old World liystricomorplis, the Hystricidae and certain Octodontidi\3, 

 and the early Tertiary Theridomyidce of Europe have been considered 

 ancestral to the group, but they have no significant relations to the Antil- 

 lean genera and their affinities are disputed, so that they may be passed 

 over for the present problem. 



The Antillean liystricomorplis are clearly related to the Soutli Amer- 

 ican types, but it is equally clear that the relationship is not close. There 

 are apparently three groups. One, including Amhlyrliiza of Anguilla, 

 Elasmodontomys and Heptaxodon of Porto Eico, is related to the chin- 

 chillas, but not closely related. Anthony* places them in separate sub- 

 families. Miller^ states that they are more nearly related to the extinct 

 Meg amy s and its allies than to the living chinchillids. These genera 

 {Megamys, Tetrastylus, etcetera) are found in the Entrerian, Eio 

 Negran, Hermosan, and Araucanian formations of Argentina accom- 

 panied by a fauna which is closely related to the Pampean, but contains 

 a few little altered survivals from the Santa Cruz Miocene and compara- 

 tively few of the North American invading types. All sliould, in my 



8 Except Leidy's Hystrix (Hystricops) vemista, based on two teeth of doubtful affini- 

 ties and uncertain geologic age. 



* Antlionj' : New fossil rodents from Porto Rico, Bull. Am. Mus. Nat. Hist., vol. 

 xxxvii, 1917, pp. 185-186. 



"Miller: Bones of mammals from Indian sites in Cuba and Santo Domingo. Smith- 

 sonian Miscell. Coll., vol. Ixvi, no. 12, 1916, p 3. 



