SOUTH AMERICAN CHAR ACID FISHES — WEITZMAN 137 



This bone has bilateral posterior lamellae projecting backward under 

 the frontals and contacting the dorsoanterior portion of each lateral 

 ethmoid. The ethmoid probably is mostly of supraethmoidal (der- 

 methmoidal) origin, but an anterior, ventral lamella of the ethmoid 

 that extends inferiorly and posteriorly to contact the prevomer below 

 is probably of endochondral origin. The ethmoidal spine found in 

 most characids (see Weitzman, 1962, figs. 2, 3, 4 of Brycon meeki) is 

 reduced to a very small structure. The premaxillaries are not firmly 

 attached (the joint being a loose syndesmosis) and are somewhat 

 movable, being attached to the ethmoid by fairly long, lax ligamentous 

 tissue. They cannot, however, be described as protractile. The 

 cartilagenous part of the ethmoid is restricted to the area between 

 the large prevomer and the ethmoid. A few foramina are present on 

 the dorsoanterior surface of the ethmoid. All species of Nannostomus 

 and Poecilobrycon have a very similarly shaped ethmoid; however, 

 members of the genus Nannostomus have a shorter snout and, there- 

 fore, a shorter, more blunt ethmoid than members of the genus 

 Poecilobrycon. 



The large ethmoid of the genera Pyrrhulina, Copella, and Copeina 

 is very similar to that in the Nannostomina in its relationships to the 

 prevomer, lateral ethmoids, and frontals. It differs, however, in 

 having a broader, more rounded horizontal profile and a very well- 

 developed, though rather obtuse, ethmoidal spine. In the Pyrrhuli- 

 nina the premaxillaries are attached to the ethmoid by a very slightly 

 movable syndesmotic fibrous joint. The ethmoid of Lebiasina and 

 Piabucina is generally similar in structure to that of Pyrrhulina, 

 Copella, and Copeina, but proportionately the ethmoidal spine is 

 considerably smaller. 



The ethmoids of the Lebiasinini and Pyrrhulinina differ most promi- 

 nently from those of the Nannostomina in the following manner: The 

 ethmoidal spine is well developed, the premaxillary is firmly fixed to 

 a groove along the anterolateral border of the ethmoid by a tight 

 fibrous joint, and the ethmoid bone is not as oblong or square in 

 horizontal profile, being somewhat more wedge-shaped. 



The ethmoid of Hoplias (Starks, 1926, p. 160, fig. 8) and Erythrinus 

 is quite similar in general form to that of Brycon (Weitzman, 1962); 

 however, the joint between the ethmoid and prevomer is bordered by 

 a lateral lamina of cartilage that is in contact with, or approaches, a 

 mass of cartilage on the medial anterior border of the palatine (fig. 

 4). In the Characinae, only very small amounts of cartilage exist in 

 these areas. The ventral diverging bony ethmoid lamellae, so well 

 developed in the other characid fishes examined, are not at all, or only 

 weakly, developed in the Nannostomina, only weakly so in the Pyr- 

 rhulinina and the Lebiasinini, but well developed in the Erythrininae. 



