6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 



length of mandible, 58+ ; depth of mandible through articular proc- 

 ess, 16.6; mandibular toothrow (alveoli), 23.8; crowp of nij, 5.8 x 5.6. 

 The material now at hand shows that the teeth of Plagiodontia 

 were correctly figured by F. Cuvier. In the maxillary teeth the struc- 

 ture is uniform throughout the series though the size diminishes 

 sensibly from first to fourth. The crowns are squarish in outline. 

 From the postero-internal corner a narrow, parallel-sided reentrant 

 fold extends diagonally across to near middle of anterior border. A 

 similar fold parallel to the last extends backward from antero- 

 external corner of crown and comes almost in contact with enamel 

 of posterior border of tooth. No trace of other folds can be detected. 

 In the mandibular teeth the premolar differs from the molars in the 

 conspicuous narrowing of its anterior half. The pattern of all four 

 teeth is fundamentally the same. On outer border there is one re- 

 entrant fold, directed slightly backward and extending less than half-' 

 way across crown. On the inner side there are two reentrant folds, 

 each much longer than that of opposite side. The tip of the posterior 

 inner fold comes nearly or quite in contact with that of outer fold. 

 The obliquity of the folds in the upper teeth is so much greater 

 than in the lower teeth that it produces an apparent lack of harmony 

 between the two patterns. As I have already remarked the enamel 

 patterns in both Plagiodontia and Isolohodon are specializations of 

 a type like that found in the Miocene Scleromys. 



BROTOMYS, gen. nov. 

 (Plate I, fig. I) 



Type. — Brotomys voratus sp. nov. 



Characters. — A spiny-rat about the size of Proechimys canicollis; 

 skull differing from that of Proechimys and other living members 

 of the group in the shorter rostrum and the greater breadth and 

 depth of both rostrum and interorbital region ; antorbital foramina 

 very large, with no trace of secondary canal for nerve ; posterior 

 emargination of palate extending forward to middle of m^ ; teeth 

 weak, the roots of incisors producing no swelling on sides of maxil- 

 laries, the cheekteeth subterete, each with three poorly developed 

 roots ; toothrows nearly parallel ; enamel pattern of pm* and m^ 

 (much worn) consisting of a single median reentrant fold from each 

 side,^ the tip of the outer fold curving back behind that of the inner. 



' A minute enamel lake lies close to the inner e.^tremity of the outer fold. 

 This lake may indicate that the complete pattern is less simplified. 



