SOUTH AMERICAN CHARACID FISHES — WEITZMAN 139 



the epiphyseal bar is relatively small in size. lu young specimens a 

 well-developed fontanel is present. A specimen 14.8 mm. in standard 

 length had a well-developed fontanel while a specimen 21.8 mm. in 

 standard length had none. The supraorbital laterosensory canal in 

 the frontal has the normal characid com'se but with the following 

 exceptions : The portion of the canal that normally is buried in frontal 

 bone over the epiphyseal bar (the mesial or epiphyseal branch) is 

 reduced greatly in length, and the canal that in the Characinae passes 

 backward in the frontal to the pareital (the posterior branch) is 

 absent. 



The distribution of major laterosensory canals is the same in the 

 frontal of the Pyrrhulinina as in the Nannostomina although the 

 mesial branch (supraorbital commissure of Branson and Moore, 1962) 

 sometimes is developed better in the Pyrrhulinina. In Piabucina the 

 posterior branch is present but it does not reach the parietal. In 

 both Lehiasina and Piabucina there is a branch of the dermopterotic 

 sensory canal extending backward in the lateralmost edge of the 

 frontal. Posteriorly the dermopterotic canal enters the pterotic. 

 Anteriorly this canal enters the infraorbital canal. In Hoplias, 

 Erylhrinus, and Hoplerythrinus the lateral edge of the frontal bone 

 extends outward to contact the spinous process of the sphenotic, 

 completely covering and encircling the dilator groove. This is not 

 true in the Characinae, nor in the Lebiasinini, Pyrrhulinina, or 

 Nannostomina. In these fishes the dilator groove is covered but not 

 encircled by the frontal. Small specimens of Hoplias have the 

 frontals and parietals separated by a fontanel, whUe adults do not. 

 In Hoplias and Erylhrinus the supraorbital sensory canal is the same 

 as in the Nannostomina, but the posterior branch extends into the 

 parietal. 



The supraoccipital of Poecilobrycon harrisoni is not unlike that of 

 Brycon in its position and relationships to other cranial bones. The 

 supraoccipital of the Pyrrhulinina, Lebiasinini, and Erythrininae is 

 quite similar to that of the Nannostomina and differs mainly from the 

 Characinae in the replacement of the supraoccipital spine with a 

 crest. 



The exoccipitals, basioccipital, and epiotics of Poecilobrycon har- 

 risoni are very much like those of the members of the Characinae and 

 differ in a manner correlated with the widening and flattening of the 

 skull. This may best be seen by comparing the illustration in 

 Weitzman (1962, fig. 5) with figure 5 of the present work. The 

 myodome is much reduced in its vertical depth. The exoccipitals, 

 epiotics, and basioccipital of the Pyrrhulinina, Lebiasinini, and 

 Erythrininae differ from those of the Characinae in having shapes 

 similar to those of the Nannostomina. 



