Crossorhombus Regan, 1920

Amaoka, Kunio & Ho, Hsuan-Ching, 2019, The lefteye flounder family Bothidae (Order Pleuronectiformes) of Taiwan, Zootaxa 4702 (1), pp. 155-215 : 177

Crossorhombus Regan, 1920

Crossorhombus Regan, 1920:211 . Type species: Platophrys dimorphus Gilchrist, 1904 .

Diagnostic features. Body deeply ovate. Tip of isthmus below middle of lower eye. Sexual dimorphism and ontogenetic changes evident on head profile, head spines, interorbital width, and length of pectoral-fin rays. Strong rostral spine in males, absent in females, and in juveniles of both sexes. Front margin of head steeper in mature males than females and juveniles. Interorbital space widely concave, becoming wider with growth, and wider in males than in females and juveniles.

Mouth rather small in size, upper-jaw length on ocular side 5.3–7.9% SL (3.0– 4.5 in HL); maxilla extending to or slightly beyond anterior margin of lower eye. Teeth on upper jaw uniserial or biserial anteriorly; uniserial on lower jaw. Scales ctenoid on ocular side with row of long ctenii along posterior margin; cycloid on blind side; 46–63 scales in lateral line. Lateral line on ocular side curved above pectoral fin; lateral line absent on blind side.

Dorsal-fin origin on blind side in front of upper margin of lower eye. Anal-fin origin below anterior base of pectoral fin on ocular side. Pelvic fin on ocular side originating at tip of isthmus, fourth or fifth fin ray opposite of first ray on blind side. Caudal skeleton with four plates including parhypural and three hypurals, all plates or only parhypural and uppermost hypural without deep clefts.

Remarks. Crossorhombus is closely related to Engyprosopon as evidenced by similar body shape, mouth size and presence of sexual dimorphism on rostral spine and interorbital width. Crossorhombus can be distinguished from Engyprosopon in having ctenoid scales with long ctenii, blind side of body stained with dark blue in male, and all four plates or uppermost and lowermost plates of caudal skeleton without deep clefts.