Amadon, D., and Short, L. L. (Ametican Museum of Natural History, New York, New York 10024) 1976. Treatment of subspecies approaching species status. Syst. Zool. 25:161167.-Speciation phenomena are discussed with special consideration of those taxa that are near the species-level borderline. Such forms, when judged to represent full species, have been termed "allospecies," and are designated by use of brackets (Amadon, 1966). There is a need to designate and treat the complementary phenomenon, namely those well-marked forms approaching the level of species, but nonetheless judged to be conspecific. To fill this void we suggest employment of parentheses to designate these latter forms, and we offer "megasubspecies" as a term for them. For example, one can treat the Savannah Sparrow, Passerculus (sandwichensis) sandwichensis, citing its various minor subspecies in the usual way, and, as a megasubspecies, the "Ipwich Sparrow," Passerculus (sandwichensis) princeps, a distinctive isolate that often is considered a separate species. Other examples are provided to illustrate the use of parentheses for megasubspecies as an adjunct to the use of brackets for designating allospecies of superspecies. It is hoped that the use of parentheses for megasubspecies will prove as useful in preparing checklists, in zoogeographical analyses, and in other ways as are brackets for designating allospecies. [Speciation; Megasubspecies; Intraspecific taxa; Superspecies.] When a species becomes divided into more or less isolated sub-populations, the latter initially vary genetically because of differences in the original founding individuals (founder principle, Mayr, 1954:169170). Subsequently, differentiation will continue at varying rates so long as these populations remain more or less isolated geographically. In determining whether the more distinct among the hundreds of such isolates have crossed the barrier separating subspecies from species, the systematist is confronted with a paradox, for although species thus evolve in isolation, it is as a rule only through the loss of this isolation that proof of their status is forthcoming. The crucial question is-would such former isolates maintain their genetic integrity and coexist with their nearest allies if they become parapatric or sympatric? In any event, the taxonomist is faced with the task of evaluating numerous taxa that are still geographically isolated-are these species or subspecies? He brings to bear on this problem every shred of evidence (often circumstantial) available from the taxa in question, and from related species, aware that it is as great an error to reduce to subspecies those taxa that have attained the species level, as it is to elevate subspecies' to the level of species. When study of two or more complementary, allopatric taxa results in the judgment that they have attained species status, 'We take it for granted that formally named subspecies are a useful taxon that will continue to be employed. This is not the place to argue the point, but a few comments are in order. Since many, some would say all or most, species of sexually reproducing organisms originate by the accumulation of genetic differences in isolated populations, it is necessary to call attention to such populations once they have become so distinct as to represent a unique ensemble of characters, morphological or physiological, or both. When these populations must be considered in large numbers, as by those studying geographical centers of origin, or parallel adaptations correlated with climate or vegetation, -for example, there is no more convenient way of doing so than by named subspecies. Trinomials so used have the great advantage of being couched, like the Linnaean system generally, in a "dead" language that until now has been spared the vagaries of an increasingly fragmented and chauvinistic world; that is, they have universal currency. Those who by inclination or by the nature of their researches have no need for the use of formal subspecies ought not to judge them useless for those who do find them useful.