NO. 3 THE RELATIONSHIPS OF QUEMISIA GRAVIS — RAY 7 



In these forms the labial reentrant lies anterior to the posterior 

 lingual one (Plagiodontia, Capromys), abuts it (Isolobodon), or 

 merges with it (Aphaetreus) . An isolated posterior enamel island 

 is thus produced in Aphaetreus, superficially as in Quemisia but 

 actually through the confluence of two folds, not the complete pene- 

 tration of one. The lingual folds in Plagiodontia and the labial 

 fold in Isolobodon and Aphaetreus approach those of Quemisia most 

 closely in compression and depth of penetration, and although the 

 approach is not very close, it is not so remote in this respect as 

 are these genera from Capromys. 



The posterior enamel wall of each reentrant fold in Quemisia is 

 extremely thin and in places not certainly detectable owing to 

 damage to the occlusal surface. Similar, but less radical, thinning 

 is characteristic of Elasr.iodontomys but has been observed in no 

 Antillean capromyid. 



Among the most striking features of Quemisia, Miller (1929a, 

 p. 24) noted that "the forward turning of the enamel folds so that 

 the anterior portion of each fold is approximately parallel with 

 the main axis of the toothrow is a specialization of high degree 

 and very peculiar kind." This character is especially well shown 

 by a sharp flexure of the posterior (here posterolabial) wall of 

 each tooth, marking the "forward turning." A similar flexure is 

 present on the corresponding face in Plagiodontia, but it is not well 

 shown by the reentrants. Differences in enamel configuration be- 

 tween Quemisia and Plagiodontia appear to be no greater than be- 

 tween the latter and Capromys. 



The discovery of a new species of capromyid (Ray, 1964a), 

 assigned tentatively to Plagiodontia and based unfortunately on a 

 single tooth (DP 4 ?), narrows the structural gap between the den- 

 tition of Quemisia and that of capromyids. The new species has 

 the crown of the tooth compressed perpendicular to the reentrant 

 folds, and the deeply penetrant, much compressed reentrant folds 

 oriented strongly anteroposteriorly. 



As part of a general survey of Antillean capromyids, the above 

 comparisons and those presented in table 1 were written in essen- 

 tially their present form on the basis of the type description of 

 Quemisia gravis at a time when the type specimen was temporarily 

 unavailable. Subsequent availability of the type has not materially 

 altered these observations, but X-rays of it have augmented them 

 startlingly (fig. IB). The first cheektooth is a deeply worn DP 4 

 with long slender anterior and posterior roots curving about a 



