FLATFISHES (HETEROSOMATA) 



Genus My ONCOI'TERUS. 



Oncoptenis, Steindarhiicr, IS75, SitzHiT. Ak.ul. Wiss. \\ leii, Ixx (i|. p. 363 [Oiicn/tlfrus darwinU, 



Steindachner]. 



Body ovate, compressed. Eyes on the right side, separated by a shghtly concave 

 space of moderate width, the upper at some distance from edge of head ; snout, 

 jaws, interorbital space and upper parts of eye-balls not scaled ; nasal organ of blind 

 side nearly opposite to that of ocular side; olfactory laminae rather numerous, arranged 

 transversely to or radiating from a long central rachis. Mouth of moderate width, the 

 jaws stronger on blind side and rather curved ; teeth small, pointed, not enlarged 

 anteriorly, in narrow bands in both jaws, better developed on blind side ; vomer 

 toothless. Gill-rakers of moderate length, rather stout, few in number ; lower 

 pharyngeals rather broad, scarcely approximated, each with several rows of small 

 pointed teeth ; branchial septum perforated by a large foramen between the lower 

 pharyngeals and urohyal. Donsal fin commencing above no.striIs of blind side and 

 well in front of eye ; first ray enlarged, stiff, curved, movable, connected with first 

 strongly developed basal bone of the fin, contained in a deep groove on blind side 

 of head level with upper eye ; most of the other rays forked distally, not scaled ; 

 no sheath covering basal part of fin. Anal similar to dorsal ; tip of first interhaemal 

 spine projecting in front of fin. I'ectoral fins unequal, that of ocular side larger ; 

 middle rays branched. Both pelvic fins developed, each with 6 rays ; that of ocular 

 side elongate, free from anal, the rays widely spaced, the last in advance of first ray 

 of that of blind side, which has a very short base. Caudal with the middle rays 

 branched : caudal peduncle short. Scales small, adherent, not very well imbricated, 

 cycloid. Lateral line with a distinct curve above the pectoral fin ; several supra- 

 temporal accessory branches and others running transversely from main lateral line 

 to dorsal edge of body. Vent on blind side, just in front of anal fin ; intestine short. 



h single species from south-eastern South America. 



1. ONCOPTERUS DARWINU, Steindachner. 



Uhombus sp., Jenyns, 1842, Zool. Voy. " Beagle ", iv, Fish., p. 139. 



Oncopterus darwmii, Steindachner, 1875, SitzBer. Akad. Wiss. Wien, Ixx (i), p. 363, pi. i ; Jord.m 



and Goss, 1889, Rep. U.S. Com. Fish., xiv, (1886), p. 281 ; Perugia, iSgl, Ann. Mus. Stor. nat. 



Genova, (2) x [xxx], p. 629 ; Berg, 1895, An. Mus. nac. B. Aires, iv, p. 7S ; Ril.eiro, 1915, 



Arch. Mus. nac. Rio de J., .xvii, Heterosomata, p. 16. 



