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For two callianassid shrimps, Nihonotrypaea japonica (Ortmann) andN. harmandi (Bouvier), morphometric character variations [carapace length (CL), eyestalk width (EsW), cornea width (CoW), and rostrum angle (RA)] were examined based on the materials collected from sandflats in western Kyushu, Japan. AUometric relationships were established between each combination of two morphometric characters for each species, in which CL was fixed on the abscissa as a reference variable. The values of EsW and CoW linearly increase with the CL value, with the slopes similar for EsW between the two species and a steeper slope for CoW in N. harmandi. By using the combination of (CoW/EsW) ratio vs. CL and that of RA vs. CL, bivariate discriminant analyses were run to establish an appropriate function separating the two species in each combination. The relatively smaller cornea size in N. japonica and more acute rostrum angle in N. harmandi were confirmed as the two effective characters that separate the two species. On the basis of the overall misclassification probabilities, the linear discriminant function using (CoW/EsW) ratio and CL was regarded as best to correctly separate the two species for practical use. Callianassid ghost shrimps are one of the most common members of the marine macrofauna worldwide, occurring from sublittoral to estuarine intertidal sediments. In western Kyushu, Japan, the second author (AT) and his colleagues have studied various aspects of the biology of a callianassid species, originally identified as Callianassa japonica Ortmann, inhabiting an intertidal sandflat (called the Tomioka Bay sandflat) in the estuarine system ranging from Ariake Sound (estuary) through Tachibana Bay (intermediate waters) to the East China Sea (open sea) (see Figs. 1 and 2 in Tamaki and Miyabe, 2000), including the species' population ecology and bioturbating effects on the benthic community structure (e.g., Tamaki et at., 1997, 1999; Tamaki and Miyabe, 2000; Flach and Tamaki, 2001). Until recently, it was believed that two species of Callianassa commonly occurred in intertidal habitats in Japan: C. japonica Ortmann, 1891, and C. petalura Stimpson, 1860 (see Sakai, 1969). However, in their taxonomic revision of these species. Manning and Tamaki (1998) revealed that Sakai's "C. japonica" was in fact a mixture of C. japonica and C. harmandi Bouvier, 1901. This was based on the description by de Man (1928) who recognized the distinction of the two species but assigned the wrong (i.e., reverse) name to each of them. Manning and Tamaki (1998) had access to the type specimens of the two species to solve the taxonomic confusion. They also proposed a new genus, Mhonotrypaea, to include the three Japanese species. Now all the material studied on the Tomioka Bay sandflat has proven to be hi. harmandi (Tamaki et al., 1999). Based on a small set of specimens, Manning and Tamaki (1998) stated that Mhonotrypaea harmandi and Â . japonica could be distinguished by the size of their cornea alone (see Fig. 1): in Â . harmandi the cornea is relatively large, at least half the width of the eyestalk, whereas in N. japonica the cornea is much smaller, one-third to one-fifth the width of the eyestalk. These characteristics could be used during the extensive survey of the distribution of the two species in the above-mentioned estuarine system [sec Fig. 8 in Tamaki et al. (1999) and Fig. 2 in Tamaki and Miyabe (2000)]. It was revealed that adults of N. harmandi mainly occurred in the coastal waters of the East China Sea plus Tachibana Bay plus the outermost onethird part of Ariake Sound, while those of A'. japonica occurred in the middle one-third part of Ariake Sound; there was a little overlap

Bivariate Discriminant Analysis for the Identification of Nihonotrypaea Japonica and N. Harmandi (Decapoda: Thalassinidea: Callianassidae)