SOUTH AMERICAN NEMATOGNATHI. 145 



Head 5; depth 8; D. 7; A. 24. 



Two specimens .045-. 05 m. Maldonado. Th. Carey. 



XVIII. ACENTRONICHTHYS. 



Acentvoniddhys E. & E. Proc. Cal. Acad. Sci. 2d Ser. i, 

 28, 1889 {A. leptos). 



Type: Acentronichthys lej^tos E. & E. 



Caudal widely forked; occipital process small, not con- 

 tinued to the dorsal; fontanel extending to the base of 

 the occipital. Orbit without a free margin. Dorsal and 

 pectorals without spines; ventrals under anterior half of 

 dorsal; anal long. Allied to Heptapterus. 



ANALYSIS OF THE SPECIES OF ACENTRONICHTHYS. 



a. Adipose fin confluent with the caudal fin; first ventral ray below third 



dorsal ray; origin of anal slightly behind origin of adipose. D. 7; A. 



19. Head 1\. leptos 104. 



rt«. Adipose fin not confluent with the caudal fin, its distance from the 



caudal equal to the length of its base; first ventral ray in front of the 



vertical from origin of dorsal. 



h. D. 7; A. 18. Depth more than 2 in the head, which is 6 in the 

 length. surinamensis 10.5. 



hb. D. 8; A. 20. Head 5-6; depth 8-9; caudal forked, the upper lobe 

 much the longer; anal fin long and low, its origin midway between 

 end of dorsal and origin of adipose. (Steindachner.) colleiiii 106. 



104. Acentronichthys leptos. 



E. & E. Proc. Cal. Acad. Sci. 2d Ser. i, 29, 1889 (Sao Matheos). 

 Type: No. 7532; one specimen .105 m. Sao Matheos. Hartt & Cope- 

 land. 



Extremely elongate, the depth of the caudal peduncle 

 not much less than the greatest depth. Head long and 

 narrow, not greatly narrowed forward, its w^idth If in 

 its length. Cheeks steep. 



Eye minute, one orbital diameter nearer tip of snout 

 than to end of opercle; interocular about 2 in the snout. 

 Maxillary barbels reaching beyond middle of pectoral, 

 mental and postmental beyond base of pectoral. Mouth 

 wide, terminal, the jaws equal, its width 2 in the length 

 10 



