6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 72 



transverse diameter. Mandible: Narrow sigmoid flexure and high 

 position of coronoid process, its tip almost reaching articular level; 

 greater width and nearly horizontal border of masseter ridge, par- 

 ticularly in the region beneath m2 and ma; more conspicuous pro- 

 tuberance under root of pm4; broader under surface of angular process; 

 much less oblique symphysis; protuberance marking base of incisor 

 situated at about middle of line connecting inner margin of alveolus 

 of mi with posterior extremity of symphysis instead of entad to 

 middle of nis. 



Detailed comparison with the skull of Plagiodontia sedium is 

 impossible at present. Nothing is known as to the whereabouts of 

 the two skulls collected by Ricord, and the only specimens which I 

 am able to refer to the original species are mandibles. Cuvier's 

 figure shows two characters which, if actually as represented, should 

 be diagnostic, namely, there are no postorbital processes (these are 

 always conspicuous in P. Tiylxum), and the vacuity formed by the 

 combined orbit and temporal fossa, as viewed from above, is much 

 smaller than in any of the skulls collected by Doctor Abbott. The 

 mandible of Plagiodontia Jiylseum is smaller and more lightly built 

 than that of P. sedium, but there appear to be no tangible peculiar- 

 ities in form. 



Teeth. — The teeth (pi. 1 figs, la, Ic; also Smithsonian Misc. Coll., 

 vol. 66, No. 12, pi. 1, fig. 4, December 7, 1916) differ from those of 

 Plagiodontia sedium as figured by Cuvier and Gervais and as repre- 

 sented by one mandible from San Pedro de Macoris, Dominican Re- 

 public (pi. 1, fig. 2) and six from San Michel, Haiti, in a general com- 

 pression of the crowns along the axis of the toothrow, so that the 

 grinding surface of each tooth and of the series of teeth taken as a 

 whole is noticeably shorter in proportion to its width. In the speci- 

 men from San Pedro de Macoris the length of the entire mandibular 

 grinding surface is 23.2 mm., greatest width transversely to longi- 

 tudinal axis 5.4, ratio of width to length, 23.3. In the two largest 

 specimens of P. Jiylxum (Nos. 239891 and 239893) the length is 

 21.0, the width 6.0, and the ratio of width to length 28.6. In the 

 type the same measurements and ratio are 19.0, 5.2, and 27.1 The 

 reentrant folds extending outward from the inner side of the teeth 

 are very narrow and so long that the tip of the anterior fold in nii 

 and m2 pushes across to a position where it almost fills the apex of 

 the anterior outer salient angle; the length of the posterior border of 

 this fold is conspicuously greater than the transverse diameter of 

 the crown measured in a direction perpendicular to the long axis of 

 the folds. In P. sedium the tip of the first inner reentrant leaves 

 free a definitely triangular dentine area in the apex of the anterior 

 outer salient angle, and the length of the posterior border of this 

 fold is not greater than the transverse diameter of the crown. The 



