64: Sy7iopsis of the Fresh Water Fishes, 



Nasal apertures with their common border circular, large, 

 and sitnated near the eyes, and on a line between them and the 

 snout. 



Operculum with a triangular, spiniform dilatation behind ; 

 cheeks entirely covered by the large third sub-orbital. 



Lateral line deflected for a short distance from the mastoids, 

 and thence running in a nearly straight line to the tail. 



Dorsal posterior, over the middle of the anal, with the height 

 not greatly exceeding the length. 



Anal rather long, with the height moderate, decreasing to- 

 wards the posterior termination. 



Caudal deeply forked, with the lobes subequal. 

 Yentrals very small, with the external rays longest. 



Pectorals moderate, pointed, with the external rays longest. 



We are generally averse to the dedication of groups of spe- 

 cies to individuals, and admit its expediency in only few and ex- 

 ceptional instances, but in this case we believe that we shall be 

 justified in so doing: we have taken peculiar pleasure in 

 dedicating to our excellent friend, Mr. Jackson Steward, of 

 whom we have before made mention, this most interesting 

 genus, the type of a new sub-family of the Characins, and a 

 near relation of the extraordinary fish to which we have given 

 the name of Nematopoma. Mr. Steward, animated by a laud- 

 able zeal for the increase of our knowledge of animals, and of 

 their geographical distribution, has enabled us to visit those 

 islands, from a single one of which we have succeeded in obtain- 

 ing the many new and remarkable forms, some of which this 

 memoir is designed to illustrate. We are therefore actuated as 

 much by a desire to commemorate his agency in the discovery 

 of these animals, as in gratitude to himself, by the name which 

 we have bestowed upon this genus. 



