402 Synopsis of the Fresh Water Fishes, 



margin of the operculum ; the space that intervenes between 

 them is equal to about four and a half of their diameters, and 

 that which separates them from the muzzle equals three and a 

 third diameters. 



In the males, the spines are robust, compressed, and con- 

 tained between four and a half and five times in the extreme 

 length of the body ; they are recurved at their extremities, and 

 the external sides and superior border, as well as the superior 

 half of the internal sides, are covered by rasp-like asperities ; at 

 the base of the spine on the external side, there is an elongated 

 triangular smooth space, and the lower portion of the internal 

 side is also smooth ; the internal border is entire, and not ser- 

 rated. 



The female of this species has never been seen by us. 



The radial formula is nearly the same as in the Hoplostemum 

 Icevigatum. 



D. I. 8—1. A. I. 6. C. I. 6. 6. 1. V. 6. P. I. 9. 



The color, as in the preceding species, is olive brown above, 

 with a tinge of purple on the skin of the abdomen. 



Genua. 



HOPLOSOMA, SWAINSON. 



Body oblong, compressed, highest at the anterior dorsal fin, 

 with the dorso-lateral plates overlapping each other on the 

 median dorsal line, behind the first fin. 



Head compressed, and with the profile presenting nearly the 

 form of a rectangular triangle; interparietal plate with an 

 elongated triangular posterior extension ; nuchal plates sub- 

 lateral and oblique, with the shape subrhomboidal, and with 

 the transverse and longitudinal diameters nearly equal ; they 

 are separated from each other by a median plate. 



Mouth inferior and small, and with an oval gape. 



Intermaxillaries, dentaries, and vomer smooth, or with micro- 

 scopic teeth. 



Lips thin ; the upper hardly covering the jaw ; the lower 



