SOUTH AJVIERICAN CHARACID FISHES — WEITZMAN 141 



"normal" orbitospheiioid. The orbitospheuoid does uot have a 

 foramen for the fu"st cranial nerve in the small specimens of the 

 Erythrininae examined, but it may, in larger specimens. An X-ray 

 negative of a specimen of Hoplias, 108 mm. in standard length, 

 indicates that a foramen may be included partially in the orbitospheuoid. 



Orbital bones (fig. 6). — There are six infraorbital bones in the 

 Lcbiasininae and Erythrininae. The supraorbital is absent. The 

 first and second infraorbitals in adult specimens of Poecilobrycon 

 harrisoni have a laterosensory tube imbedded within them. The 

 remainder of the infraorbital bones have the infraorbital canal along 

 their ocular edge but it is enveloped only partially in bone. Only 

 Poecilobrycon eques, P. harrisoni, and P. unifasciatus have a sensory 

 tube contained within the bony substance of both the first and second 

 infraorbitals. All other Imown members of the Nannostomina lack 

 this bony tube in the second infraorbital, the infraorbital canal 

 passing over the surface of the bone. The antorbital is present and 

 weU developed in the Nannostomina; it sometimes partially envelops 

 the anterior part of the infraorbital canal. In the Pyrrhulinina the 

 first two infraorbital bones have enclosed canals; sometimes the 

 other infraorbital bones also have enclosed canals in members of 

 this subtribe. 



In the Lebiasinini the infraorbital canal may be included within 

 the bony substance of all the orbital bones or it may pass only over 

 the surface of the second through the fifth infraorbital. It may pass 

 either within or over the substance of the antorbital. 



In the Erythrininae the orbital bones have an infraorbital canal 

 imbedded in them. There is no supraorbital; the antorbital contains 

 a canal and is fused with the first infraorbital. This is apparently 

 similar to the situation found in certain cyprinodonts and catfishes 

 (see Weitzman, 1962, pp. 28-31). Another possible interpretation is 

 that the antorbital is absent, the first infraorbital having extended 

 into the topographical area of the antorbital. 



The elongate nasal bone of the Nannostomina has the usual char- 

 acid relationship, being a tubular bone connected with, and anterior 

 to, the supraorbital canal of the frontal. In the Pyrrhulinina, Lebias- 

 inini, and the Erythrininae the nasal bone is not greatly different 

 from that of the Nannostomina except for differences correlated with 

 the broader and shorter snouts in these fishes. 



Opercular apparatus (figs. 6, 7). — The opercular bones of the 

 Nannostomina differ from those of the Characinae mainly in having 

 a different shape correlated with the elongate and relatively flattened 

 head. The thin interopercle internally covers much of the lower sur- 

 face of the symplectic, preopercle, metapterygoid, and even some of 

 the quadrate. The preopercle does not extend forward to near the 



