New World hystricognath rodents (parvorder Caviida) easily qualify as the most diversified members of the nonvolant Quaternary land mammal fauna of the West Indies. This paper describes three intriguing but problematic representatives of this group from Jamaican cave deposits. The first is the holotype (and still the only) specimen of Alterodon major from Wallingford Roadside Cave, a taxon that continues to generate controversy because specialists disagree as to its placement within Caviida. We reject the argument that it should be placed in Octodontidae and reaffirm the high probability that it is a clidomyine. The second fossil is a large proximal femur, apparently recovered from Sheep Pen locality near Windsor (Trelawney Parish) in the 1960s. Much larger than the femur of Clidomys (previously thought to be Jamaica's largest Quaternary mammal), in size and morphology the new fossil somewhat resembles femora of the eastern Caribbean heptaxodontine Amblyrhiza. Although firm allocation is not possible, the Sheep Pen femur is possibly that of a megafaunal caviidan. The third fossil described in this paper is the jaw of a previously unknown caviidan from a dated end-Pleistocene cave context in Portland Ridge (Jackson's Bay, Clarendon Parish). Xaymaca fulvopulvis, new genus and species, differs from all West Indian caviidan species presently known. The jaw is well preserved but retains only the incisor and premolar (the latter in a very worn state). The few features for which the new species can be usefully analyzed and compared to caviidan groups represented in the West Indian Cenozoic (capromyids, heteropsomyines, heptaxodontines, and clidomyines) are largely indecisive from a systematic perspective. However, on balance the strongest indicators seem to lie with the “giant” heptaxodontines of the central and eastern Caribbean (the grouping composed of Amblyrhiza, Elasmodontomys, and possibly Quemisia), and despite its diminutive size Xaymaca is tentatively placed within that group. It is increasingly apparent that much still remains to be learned about the origin and history of the land mammal fauna of Jamaica.