XANK&THIOPS. 137 



5. NANELffiTHIOPS. 



Giinther, Proc. Zool. Soc. 1871, p. 669 ; Boulenger, Poiss. Bass. Congo, p. 182 (1901). 



Mouth rather small, each jaw with two series of small, notched, bicuspid teeth ; 

 a few small teeth at the base of the maxillary bone. Cheek covered by the sub- 

 orbitals; nostrils close together, separated by a valvular flap; gill-membranes free 

 from the isthmus; 4 branchiostegal rays. Body moderately elongate, strongly 

 compressed ; belly rounded. Scales rather large, with strongly ciliated border ; lateral 

 line, if distinct, equally distant from the dorsal and the ventral outline ; a scaly process 

 at the base of the ventral. Dorsal fin with 13 to 15 rays, above the ventrals; anal 

 fin with 10 rays ; a very small adipose dorsal fin. 



A large fontanelle separates the frontal s and the parietals. The air-bladder is 

 moderately elongate, the posterior chamber about twice as long as the anterior, and 

 the intestine is shorter than the body. 



A single species is known, which may be regarded as a connecting-link between the 

 Hydrocyoninae and the Distichodontinse. 



1. NANN^THIOPS UNIT JEN TAT US. 

 (Plate XXI. fig. 3.) 



Giinther, Proc. Zool. Soc. 1871, p. 670, pi. lxv. fig. C ; Sauvage, Bull. Soc. Zool. Prance, 1882, 

 p. 321 ; Vaillant, Bull. Soc. Philom. (8) v. 1893, p. 13 ; Boulenger, Poiss. Bass. Congo, 

 p. 182 (1901) ; Lonnberg, Ann. & Mag. N. H. (7) xii. 1903, p. 38. 



Depth of body two and three-fourths to three and a half times in the total length, 

 length of head three and a half to four times. Head about twice as long as broad, 

 a little longer than deep, its upper surface rugose in the adult ; snout rounded, shorter 

 than the eye, the diameter of which is contained two and a half to three times in the 

 length of the head ; interorbital width a little greater than the diameter of the eye ; 

 mouth terminal ; 22 to 30 teeth in the outer prsemaxiliary series ; maxillary extending 

 to below the anterior border of the eye. Gill-rakers short, 10 to 12 on lower part of 

 anterior arch. Dorsal fin with III 10-12 rays, originating a little in advance of the 

 ventrals, its distance from the eye equal to its distance from the caudal fin ; longest ray 

 anterior, nearly equal to the length of the head. Adipose fin very small, once and a half 

 to twice as distant from the rayed dorsal as from the caudal. Anal fin with III 7 rays, 

 nearer the caudal than the base of the ventrals. Pectoral fin about two thirds as long 



T 



