Genus Hemitriakis Herre, 1923: 70. Type species: Hemitriakis leucoperiptera Herre, 1923, by original designation.
For detailed definitions and discussions of the scope of this genus see Compagno (1970, 1979, 1984, 1988). Hemitriakis was proposed by Herre (1923) as a monotypic genus for H. leucoperiptera Herre, 1923, from the Philippine Islands. H. leucoperiptera was included in Triakis Müller & Henle, 1838 by Fowler (1941), Bigelow & Schroeder (1948), Garrick (1954), Kato (1968), Springer (1968), and Pinchuk (1972), but was revived by Compagno (1970) for Herre's species and Galeus japanicus Müller & Henle, 1839. H. japanica, from off China, the Koreas, Taiwan and Japan, had been placed in the genus Galeorhinus or its synonyms by previous authors. The genus Hemitriakis was recognised by Compagno (1973 a, 1973 b, 1979, 1984, 1988), Steuben & Krefft (1978, 1989), Cadenat & Blache (1981), and Masuda et al. (1984). More recently, Hemitriakis falcata Compagno & Stevens, 1993 and H. abdita Compagno & Stevens, 1993 were described from off northwestern and northeastern Australia, respectively, and H. complicofasciata Takahashi & Nakaya, 2004, was described from off Japan and Taiwan. Hemitriakis indroyonoi is described herein from off eastern Indonesia. There is a second species of Hemitriakis in Philippine waters, Hemitriakis sp. A [sensu Compagno et al., 2005], differing from H. leucoperiptera in coloration and fin proportions (see Compagno 1970, 1979, 1988; Compagno & Stevens, 1993).
Fowler (1941) cited a record of Hemitriakis japanica from Amboina, while Fourmanoir & Rancurel (1972) reported H. japanica from New Caledonia. We have not been able to verify the Amboina record, but a large New Caledonian Hemitriakis was deposited by P. Fourmanoir in the Museum National d'Histoire Naturelle, Paris, as Galeorhinus japanicus. This specimen has a much higher vertebral count than all other Hemitriakis except H. abdita and may represent another undescribed species of Hemitriakis or possibly an adult of H. abdita.