22 SMITPISONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



smaller than that of the holotype. The other fragment is like the 

 holotype in the shape and position of the masseteric fossa, the loca- 

 tion of the tooth roots, and in the outline of the ramus, except that 

 it is much smaller, with a noticeably smaller incisor. P4 was 2-rooted, 

 the roots round and long. Mx-Mg was 2-rooted, with the roots broad 

 transversely. This specimen, owing to its smaller size, may indicate 

 another form present in the deposit. 



The skull fragment consists of the rostral region, the premaxil- 

 laries, nasals, incisors, and the anterior part of the maxillaries. The 

 upper incisors are the shape of those of the holotype but larger. The 

 rostrum slopes forward from the small infraorbital foramina. The 

 width of the rostrum between the infraorbital foramina is 8.5 mm. 

 The width across the incisors is 6.5 mm. The anterior palatine 

 foramina are anterior and small. They end posteriorly at the suture 

 between the premaxillaries and the maxillaries. The nasals extend 

 4.2 mm. posterior to the infraorbital foramina. They are long, rec- 

 tangular in shape, and do not noticeably flare transversely at their 

 anterior tip. The upper incisors are as much larger than the upper 

 incisors of the holotype, as the lower incisor in the fragmentary ramus 

 is smaller than the holotype. From all characters present it appears 

 that the rostral region of the skull belongs to a specimen of Flores- 

 omys or a closely related form. This rodent very likely grew through- 

 out much of its life like many of the gophers and beavers, and the 

 size difference shown by the fragmentary material is that of individual 

 age. 



Discussion. — Floresomys guanajuatoensis is placed in the sub- 

 family Sciuravinae on the basis of the distinct cusp development and 

 the reduction of conules (Wilson, 1949, p. 96). Floresomys is dis- 

 tinct from the other known genera of Sciuravinae by the presence of 

 the broad deep valleys separating the paracone and protocone from 

 the metacone and hypocone and the metaconid and protoconid from 

 the entoconid and hypoconid, as well as by the absence of a true meta- 

 conule, mesostyle, mesoconid, and mesostylid. It is probably more 

 closely related to Taxymys than to any of the other genera, but it 

 still represents a distinct line of rodents. Robert W. Wilson, in a let- 

 ter which clearly expresses the position of the specimen, made the fol- 

 lowing comment in regard to the holotype: "In many ways this 

 rodent is similar to but somewhat more advanced than Sciuravus 

 pozvaycnsis of the early late Eocene [on the vertebrate paleontologist's 

 time scale] of southern California. In one presumable fundamental 

 character, however, it is more like Taxymys (middle Eocene) than 



