24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



early Bridgerian to early Uintan, inclusive. If 'Sciuravus' depressus 

 is a sciuravine, the downward limit is middle Wasatchian. Records 

 of the group later than early Uintan are vague, but Burke (1934, p. 

 391) speaks of teeth of the Sciuravus type persisting into the basal 

 Duchesne River beds." Gazin (1952, p. 48) records Sciuravus from 

 the La Barge fauna from Wyoming (late Wasatchian). 



If Floresomys did branch off from the Taxymys stock, its special- 

 ized development could have occurred during the late Eocene. If 

 Floresomys is more closely related to the Sciuravus powayensis 

 Wilson (1940) line, there is still no morphological evidence that it 

 is younger than late Eocene. 



The dentition of Floresomys is reminiscent of the Heteromyidae, 

 although the diastema and the M^ rule out such a relationship unless 

 it was very early in the development of the Geomyoidea. 



Wilson (1940) described Griphomys aleccr from the Eocene (Tapo 

 Ranch fauna of California), which may be a Geomyoidea. There is 

 some similarity between Griphomys and Floresomys in the develop- 

 ment of the deep transverse valley that divides the tooth into anterior 

 and posterior parts. It may be that Floresomys is a descendant of a 

 generalized paramyline stock and that the dental pattern is a simpli- 

 fication of the paramyline tooth pattern. If such is the case Flores- 

 omys would not be expected to be younger than Griphomys. The de- 

 velopment of the lower jaw, and of the lower and upper dentition, 

 indicate a form no younger than earliest Oligocene. 



In the comparative study of these specimens the aberrant Kan- 

 sasimys (Wood, 1936) from the middle Pliocene of Kansas should 

 be noted because of its probable relationship to the Ischyromyidae. 

 Kansasimys presents certain specialized characters that distinguish it 

 from the early Ischyromyidae and Floresomys. The more generalized 

 characters of the lower jaws and rostral region of the skull (?) of 

 Floresomys indicate a much greater antiquity than that of Kansasimys. 



The tapiroids of North America (north of Mexico) are known 

 from the lower Eocene to the Pleistocene. The generalized characters 

 and small size of the tapiroid foot can be taken to indicate an age no 

 younger than earliest Oligocene for the deposit. 



LITERATURE CITED 



Arellano, Alberto R. V. 



1952. El hallazgo de mamiferos del Cenozoico inferior en el conglomerado 

 rojo de Guanajuato. Bol. Asoc. Mexicana Geologos Petroleros, 

 vol. 4, Nos. 1-2, pp. 63-64. 



