GLIRES OF THE SANTA CRUZ BEDS. 395 



a more steeply inclined dorsal border than in the modern genus. The 

 inferior dental foramen has the same position as in Myocastor. 



Vetebral Column and Ribs (Plate LXX). Except for the cervical and 

 some of the lumbar vertebrae, the backbone is represented by very unsat- 

 isfactory material and the vertebral formula is largely conjectural. The 

 neck is short, but relatively stout, its proportions being not .unlike those 

 of the neck in Agouti. The atlas most resembles that of Capromys ; it is 

 short, broad and depressed, with low and wide neural canal ; the neural 

 spine is a prominent tubercle and there is a distinct hypapophysis ; the 

 transverse processes are very different from those of Myocastor, resembling 

 rather those of Agouti, except that they are considerably shorter. The 

 axis has a neural spine which is quite like that seen in Capromys and 

 Myocastor, but it is produced more obliquely upward and less backward ; 

 the centrum, which is keeled ventrally, is very broad and depressed an- 

 teriorly, becoming much narrower behind the transverse processes, which 

 are short and slender. The remaining cervicals are not especially char- 

 acteristic ; they have short and depressed centra, with very oblique faces, 

 and short neural spines, of about the same relative size as in Agouti; the 

 transverse processes, on the other hand, are much smaller and the " inferior 

 lamella" is distinct only on the sixth. 



The number of trunk vertebrae is very uncertain, but there is reason to 

 believe that the formula is not far from Th. 13, L. 6. In the anterior 

 thoracic region the vertebrae are small, with slender neural spines inclined 

 strongly backward ; the spine of the second thoracic appears to have been 

 considerably stouter than that of the first or the third, but not to any such 

 disproportionate extent as in Myocastor. Posteriorly the vertebrae be- 

 come much larger, gradually assuming the character of the lumbars. In 

 the latter, the centra are long and heavy, with ventral keels and expanded, 

 depressed faces, and have long, broad and laterally compressed neural 

 spines, much resembling those of Agonti in shape and, as in that genus, 

 strongly inclined forward ; the prezygapophyses are very prominent, but 

 the metapophysesare small and do not rise conspicuously above them; 

 the anapophyses are likewise small, a striking contrast to Myocastor, in 

 which these processes are remarkably long and prominent. The trans- 

 verse processes are not complete in any of specimens and their length 

 cannot be determined, but so far as they are preserved, they resemble 

 those of Agouti; in fact the lumbars are decidedly more similar to those 

 of the latter than to those of Myocastor. 



