D SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IIO 



coast of tropical America, which also has a ligament between the 

 maxillary and premaxillary, but furthii has more ventral scutes (34 

 to 2>7), and the ventral fins are inserted farther forward, being equi- 

 distant from the base of the pectoral and origin of the anal in furthii, 

 whereas they are inserted notably nearer the origin of the anal than 

 the base of the pectoral in apapac. 



The name, apapae, is from apapa, used in Brazilian publications as 

 a name for fresh-water herrings. 



NEOOPISTHOPTERUS, new genus 



Genotype. — Odontognathus tropicus Hildebrand, U. S. Nat. Mus. 

 Bull. 189, p. 94, fig. 19, 1946, Puerto Pizarro, Peru, and Balboa, 

 Canal Zone. 



This genus belongs to that group of small herrings with a strongly 

 compressed body, a long anal fin which begins in advance of the 

 dorsal fin, and in which the ventral fins are missing. Consequently, 

 the relationship of this genus is with Opisthopterus and Odontogna- 

 thus. From these genera it differs importantly in the structure and 

 relative position of the maxillary and premaxillary. In the two old 

 genera mentioned these two elements are separated by a short tooth- 

 less membranous section (hitherto undescribed). The margin of 

 the upper jaw, nevertheless, is continuous (uninterrupted). In the 

 new genus the margin is discontinuous (interrupted), as the maxillary 

 definitely overlaps the premaxillary, that is, it extends over the distal 

 end of the premaxillary (fig. 4). Opisthopterus and this new genus 

 agree in having a relatively short maxillary, which does not seem to 

 be produced into a long narrow process as in Odontognathus (at least 

 there is no indication in the rather small specimens, up to 66 mm. in 

 standard length, of Neoopisthopterus at hand, that this element will 

 become produced with age and growth). Furthermore, in Opis- 

 thopterus and the new genus the margins of the ventral scutes are 

 entire (smooth), whereas the margins of the posterior ones in 

 Odontognathus are sharply serrate. The teeth in Neoopisthopterus 

 are all small to minute, and are present on the jaws, palatines, ptery- 

 goids, and tongue, but missing on the vomer. Vertebrae about 46 

 or 47. 



The anal fin in the two known species of this genus is shorter than 

 in the related genera, being composed of 39 to 48 rays, whereas the 

 species of the genus Opisthopterus have about 56 to 65 rays, and 

 those of Odontognathus about 58 to 78. 



The close relationship betwen this new genus and Opisthopterus 

 suggested the name, Neoopisthopterus, that is, a new Opisthopterus. 



