144 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lie 



lower jaw. Althougli examination shows that Characidium has a 

 distinctly two-headed hyomandibular, that in the Nannostomina 

 is single-headed. The hyomandibular in the Nannostomina is a 

 broad bone with a broad dorsal articular surface that articulates 

 with both the sphenotic and pterotic. It does not differ greatly in 

 shape or relationships from the hyomandibular in the Characinae. 

 The hyomandibular is not markedly different in shape or functional 

 relationships in Pyrrhulinina, Lebiasinini, or Erythrininae. 



The quadrate of Nannostomus and Poecilobrycon is a large, rather 

 rectangular bone with a long, slender posterior process below the 

 symplectic. The dorsal surface of the quadrate extends upward, 

 lateral to the large mesopterygoid, and the dorsal profile of the 

 quadrate is gently curved. The posterior upper surface contacts 

 the metapterygoid and anterior end of the symplectic thi-ough 

 cartilage. The symplectic is quite large, elongate, and rather slab- 

 shaped posteriorly. It is almost as long as the hyomandibular. 

 The metapterygoid posteriorly contacts the lower end of the hyo- 

 mandibular through cartilage. The central circular fenestra between 

 the quadrate, symplectic, and metapterygoid, so typical of almost all 

 other characids, is absent in the Nannostomina. Just anterior to 

 the upper anterior corner of the quadrate is a smaU triangular ecto- 

 pterygoid. In some members of the Nannostomina, this bone bears 

 a few simple conical teeth. In one species, Poecilobrycon egues, 

 teeth were foimd on the ectopterygoid of one side but not the other 

 in some specimens. 



The toothless palatine is well developed and hes lateral to the 

 pre vomer. The anterior head of the palatine Hes just posterior to 

 the upper process of the maxiUary. 



The mandibular and palatine arches in the Pyrrhulinina and 

 Lebiasinini examined are very similar to those in the Nannostomina, 

 but, in general, these bones are not as elongate as in the Nannostomina. 

 The ectopterygoid is toothless in the Pyrrhulinina but has conical 

 teeth in the Lebiasini, and the bone is always proportionately larger 

 than in the Nannostomina. The fenestra between the quadrate, 

 symplectic, and metapterygoid is absent. 



In the Erythrininae, the mandibular and palatine arches are 

 very similar to those of the Characinae. The fenestra between the 

 metapterygoid, quadrate, and symplectic is well developed, and the 

 symplectic is not exceptionally deep at its posterior end. In Hoplias 

 the ectopterygoid is a long, thin, tooth-bearing bone extending from 

 the upper part of the quadrate across the inferior surface of the 

 palatine. Anterior to its forward boundary is a small autogenous 

 movable piece of tooth-bearing bone that is connected closely to the 

 ectopterygoid, Sagemehl (1885, p. 95) called this bone the accessory 



