Fishes of the genus Lethrinus (family Lethrinidae) are sparoids of moderate size that are very abundant in coastal waters of the tropical and subtropical Indo-Pacific. They are very popular as food fish in that area and have been attracting a great deal of scientific attention as well. Since Forsskål (1775) described four species of this genus in his "Descriptiones Animalium," many publications dealing with these fishes have appeared, and numerous specimens have accumulated in museums throughout the world. The fishes of this genus can easily be distinguished from other sparoids by several clear characteristics such as the absence of scales on the cheek and the top of the head. The intrageneric systematics within this genus, however, has been in great chaos. For example, although about a hundred species have been published, a majority of their names are junior synonyms of others, as will be shown in the present work. On the other hand, the same names have often been applied to several different species. In this group it has not been easy to find definite key characters to identify species because they look quite similar to one another superficially, especially when specimens are in a preserved condition and their color patterns have faded, while some of their characters show considerable variation within the same species. Therefore, most of the descriptions given by earlier authors have failed to supply sufficient diagnoses for their species.

The present writer has tried to improve the confused state as far as possible both by examining the real fishes carefully and by reviewing the previous works together with re-examination of type material. In this paper 26 species are described as valid, including one new species mentioned below, and a key to those species is given. Only those records in which the identities of the species have been confirmed by the present writer himself are included in the synonym list for each species.

As is precisely discussed by Sato (1971: 119), many of the fishes of this genus have certain color markings or patterns characteristic of species which are always recognizable as long as the specimens are in a fresh condition (e.g., red spots on the opercle or on the base of the pectoral fin observed on some species). Sometimes these markings and patterns are less conspicuous than other patterns which are common to several or all species and have therefore often been overlooked by the previous authors. In the present work those markings and patterns are illustrated for each species.

The writer has found that there exists a popular Lethrinus species with a fairly wide distribution which has never been named. This species is especially abundant in the Bonin Islands, Japan, and has a slender body and conical lateral teeth on the jaws, The red spot on the posterior end of the opercle is one of the characteristics of this species. It is described as a new species in the present paper.

Two different species have been found by the writer among the syntypic series of L. argenteus Valenciennes, L, waigiensis Valenciennes, L. richardsonii Günther and L. Moensii Bleeker each. Lectotypes are designated for these four names in this paper.