SOUTH AMERICAN NEMATOGNATHI. 143 



Anal well developed, placed under the middle of the 

 adipose fin, the tips of the last rays reaching the verti- 

 cal from tip of adipose fin. 



Ventrals inserted under the third dorsal ray, li-l| in 

 the head. 



Pectoral spine short, with a flexible portion, which is 

 1-J times as long as the spinous portion; the spinous por- 

 tion 2J in the head; length of the pectoral fin about 

 equal to the head. 



Ground color light, the sides thickly covered with jet- 

 black dots, about six short cross-bars on the back; top 

 and sides of head profusely covered with minute black 

 dots; caudal and adipose dotted with black, other fins 

 plain. 



Head 5; depth 7*; Br. 7; D. I, 6; A. 10. 



Air-bladder narrow, reniform, its longitudinal axis 

 transverse, lying under the lateral processes of the first 

 vertebrae. 



XVII. HEPTAPTERUS. 



Heptapterus Bleeker, Ichthyol. Arch. Ind. Silur., 197, 

 1858 (mustelinus). 



Type: Pimelodus mustelinus C. & V. 



Caudal obliquely rounded. Dorsal fin without a spine, 

 placed above the ventrals. Eye small, without a free 

 orbital margin; adipose fin long and low, confluent with 

 the caudal. Air-bladder reniform. Anal rather long. 

 Fontanel very narrow, continued to the base of the oc- 

 cipital, with a narrow interruption behind the eyes. 



This genus has been placed by Dr. Giinther with his 

 Stturidce Opisthopterce; it has been entirely overlooked by 

 Gill in his arrangement of the families of fishes. The 

 fact that it possesses a free air-bladder seems to us to be 

 of much more significance than the mechanical position 

 of the dorsal or ventrals, especially as Rhamdella minuta 



