124 CALIFORNIA ACADEMY OF SCIENCES. 



Pimelodus sleyelichii Midler & Troschel, Horco Ichthyol. iii, 3, 1849 



(Surinam); Giinther, Cat. Fish. Brit. Mus. v, 121, 1864 (Dema- 



rara; Surinam). 

 Pimelodus musculus Mtiller & Troschel, Horse Ichthyol. iii, 4, 1849 



(America). 

 Pimelodus holomelas Giiuther, Ann. & Mag. Nat. Hist, xii, 1863, 



442(Essequibo); Giinther, Cat. Fish. Brit. Mus. v, 120, 1864 



(Essequibo). 

 Pimelodus m'Uleri Giinther, Cat. Fish. Brit. Mus. v, 119, 1864 



(Kiver Capin, Para; Surinam). 

 Habitat: Rio Janeiro to Rio Magdalena; Amazons to Tabatinga. 



Width below the first dorsal ray equals the depth; body 

 strongly compressed near the caudal; head flat above, 

 the sides of the head sometimes making a decided angle 

 with the top, sometimes sloping without any distinct 

 angle; greatest width of the head about 1J in its length, 

 its width at the angle of the mouth 2 in its length. Top 

 of the head covered with a usually thin skin, the surface 

 of the bones smooth in the young, becoming roughened 

 with age. Fontanels in the young, three. In speci- 

 mens .10 m. long they are reduced to a narrow slit in 

 the center of the occipital bone: this remains in the 

 adult as a circular depression; a small circular opening 

 above the posterior margin of the eye, which usually 

 disappears with age; and the usual frontal fontanel, per- 

 sistent in all stages of growth, but reduced to a narrow 

 slit with age. Occipital process extending half way to 

 the dorsal spine. Large pores regularly distributed 

 about the head, sometimes innumerable pores on cheeks. 



Eye sometimes circular, sometimes elliptical. In speci- 

 mens .10 m. the eye measures 2 in snout, 1J in interocu- 

 lar, 5 in head; in specimens .25 m. 3 in snout, 3 in. iii- 

 terocular, 7J in head. 



Maxillary barbels either compressed or filiform, ex- 

 tremely variable in length; when shortest extending to 

 the middle of the adipose fin when longest extending 

 beyond the caudal. They are longest in specimens from 

 .10 to .15 m. and are shorter in both young and adult. 



