30 ANNALS NEW YORK ACADEMY OF SCIENCES 



m^, 12.5 to 14.5; depth at coronoid process, 17 to 33; depth at condylar 

 process, 18 to 34 mm. 



The maxillary toothrow (crown surface) varies in length, in adults, 

 from 15.5 to 17 mm. ; the mandibular toothrow from 17.5 to 19 mm. The 

 teeth evidently increase in size with age, not only in length and breadth 

 but in height, becoming more hyposodont as well as larger in old adults, 

 and the angles of the folds more prominent. 



Dentition. — In Capromys the transverse axis of the molar teeth forms 

 a right angle with the axis of the toothrow; in Plagiodontia the trans- 

 verse axis of the molars is highly oblique to the axis of the toothrow 

 (Plate II, Fig. 10) ; in Isolohodon the obliquity is about 45° ^. The in- 

 cisors are weak, nearly flat on the outer face, without grooves, and rounded 

 on the inner face. Their color, still well preserved, is pale yellow. 



The molariform teeth in Isolohodon (Plate II, Figs. 5-7) resemble 

 those of Plagiodontia in size and shape, in the obliquity of their inser- 

 tion, and in the number of folds on the outer and inner borders, but not 

 at all in the enamel pattern. They are thus modeled on a basis common 

 to both types, and both thus differ widely from the teeth of Capromys. 

 In Plagiodontia the cement area of the crown surface of each tooth con- 

 sists of three transverse divisions, united and continuous, thus constitut- 

 ing a single sigmoid area, deeply cut by the infolding of the enamel 

 border. In Isolohodon the cement of the crown surface of each molar 

 forms two transverse, nearly equal oval lakes, entirely separate and encir- 

 cled by an enamel border. The enamel walls of the two loops touch each 

 other by a slight point of contact near the outer border of the upper teeth 

 and the inner border of the lower teeth. The enamel pattern of the lower 

 molars differs from that of the upper through a deep indentation of the 

 anterior enamel lake by the infolding of the enamel border on the inner 

 side of the front third of the tooth. 



All of the molars have each two vertical ribs or folds on both the ex- 

 ternal and internal borders, but the upper premolar differs from the 

 molars in having three external and two internal. The lower molars have 

 each three external and two internal folds. The lower premolar has three 

 folds on each side, but the anterior fold is greatly reduced in depth, and 

 thus gives rise to a small trefoil termination to the cro^wn surface of the 

 front border of the tooth. 



The upper teeth successively decrease in size from the premolar to m^. 



s If the upper molar series is correctly represented in Cuvier's plate, the maxillary 

 teeth in Plagiodontia have the transverse axis of the teeth nearly coincident with the 

 longitudinal axis of the toothrow, while in the mandibular series the angle is only about 

 45°, as in Isolohodon. I cannot resist the impression that the obliquity of the maxillary 

 teeth is highly exaggerated in Cuvier's drawing. 



