Andersen (1909a:216; 1912:436) considered the relationships of _Pteralopex_ and _Pteropus_ and concluded that _Pteropus pselaphon_ Lay, 1829, from the Sulphur Islands east of Taiwan, and _Pteropus samoensis_ Peale, 1848, from the Samoan Islands, were the "closest" living relatives of _Pteralopex_. He stated further that _Pteralopex_ "presents in fact scarcely a single character which is not either developed to a certain extent or at least distinctly foreshadowed in _Pteropus pselaphon_, _pilosus_, _tuberculatus_, or _leucopterus_." In summary, Andersen thought several species of _Pteropus_ had undergone evolutionary development resembling that in _Pteralopex_, and that the latter, with its massive, cuspidate cheek-teeth, could be considered a highly modified _Pteropus_. For this hypothesis to be plausible, one must assume that the originally complex cheek-teeth of pteropodids became simple and, at least in the case of _Pteralopex_, secondarily became complex once again. According to present-day theory of evolutionary development, his hypothesis is improbable. Thomas (1888b:475) probably was correct when he considered _Pteralopex_ an isolated relic.
Although _Pteralopex_ usually is listed after _Pteropus_ in phylogenetic arrangements (see, for example, Sanborn, 1931:21; Pohle, 1953:129; Laurie and Hill, 1954:40), I have placed _Pteralopex_ before _Pteropus_.
Two subspecies of _Pteralopex atrata_ (_P. a. atrata_ and _P. a. anceps_) have been named; specimens of both are rare in museum collections. Thomas (1888_a_:155) described adults of _atrata_. Sanborn (1931:21) examined the one additional specimen known to me and reported that it agreed with Thomas' description.
Andersen (1909_b_:266) used a subadult female ("nearly fully grown") as the holotype of _anceps_. At least five additional specimens, all adults, of _anceps_ now are housed in various collections. Judging from these individuals, the holotype of _anceps_ was only four-fifths grown and because he used an immature individual, Andersen's (1912:437) criteria for distinguishing the two subspecies mostly are invalid.
[Illustration: FIG. 4. Distribution of _Pteralopex atrata_; _P. atrata atrata_ ([RW]) and _P. atrata anceps_ ([BC]). For names of islands see Fig. 2.]