CONTENTS OF A BONE CAVE. 11 



A section of all except the terminal teeth is an oblique rhomboid, the longitudi- 

 nal diameter being but little greater than the transverse. A single terminal tooth 

 (either superior posterior or anterior inferior) is narrowed in the terminal column. 

 All the teeth possess one longitudinal groove on one side, and two on the other, 

 which are covered but not obliterated by the cement layer. The teeth, though 

 much straighter and more slender than those of the superior series, yet possess a 

 light lateral, though no anteroposterior curvature ; those of the upper and lower 

 series curving in opposite directions. 



Indies. 

 Length of a median molar . . . . . .1.7 



Anteroposterior diameter (oblique) ..... .52 



Transverse " (both of crown) . . . .43 



" " (terminal molar) . . . .39 



Longitudinal diameter of terminal molar .... .56 



The inner face of the incisor tooth is plane and at right angles to the anterior; 

 the outer is rounded obliquely inwards ; the inner face is broad and not prolonged, 

 the curve of the tooth is in one plane, and the depth is about equal to the width. 

 A narrow fold of the enamel embraces the anterior border of the inner and 

 outer faces; it is folded back at a right angle within, and with a truncate angle 

 without. The enamel is sculptured into numerous close, fine longitudinal grooves, 

 which do not inosculcate. The separating ridges number fourteen near the middle 

 of the tooth, those near the borders being the strongest. One, strongest of all, is 

 on the external turn of the enamel, and near it numerous interrupted ridges have a 

 slightly oblique direction. 



The incisors are, as in the modern representatives of the AmHyrliiza, of more 

 slender proportions than in the beavers, Arctomys, and other rodents, and their 

 extinct predecessors. They are therefore relatively less stout than those of the 

 Castoroides. Their sculpture is quite similar to that seen in the Lagidium and 

 other chinchillas. 



Lines. 



Width anteriorly -L . -6 



Depth ......... 5.7 



The inferior molars differ much from those of the superior series. They are 

 straight, prismatic, and composed of three dentinal columns, one of which is in- 

 curved, but none closed at the base. The triturating surface is very oblique in the 

 vertical direction, indicating the greater elevation of the teeth at one extremity of 

 the series than the other. A horizontal obliquity of the dentinal columns is pro- 

 duced by their lateral displacement. Enamel plates but slightly curved. 



Extremities. I describe under the head of this species those bones of adult 

 individuals of smaller dimensions which the different lots contain. Some of these 

 came associated with teeth of A. inundata without admixture of larger bones ; and 

 most of the larger ones came to hand with the jaws and teeth of the A. latidens and 

 of the A. quadrans. In other lots both sizes were mixed. 



A femur distinguished by its bright red color came with teeth of A. inundata 

 of the same color. The triangular form of the section of the shaft disappears a 

 short distance below the little trochanter, and is replaced by a suboval one. The 

 measurements are as follows : 



