84 



OSTEOGKLOSSIDiE. 



and anal fins nearly equally developed, on the caudal region of the body, elongate and 

 narrowly separated from the small caudal ; ventral fins nearer end of snout than caudal 

 fin. Vertebrae 27 + 42-43. Air-bladder cellular, lodged in the closed haemal arches 

 of the caudal vertebrae. Fourth branchial arch with an accessory breathing-organ. 



Pig. 13. 



Grill-helix of Ileterotis niloticus. (After Hemprich & Ehrenberg.) 



The accessory breathing-organ is a spirally-coiled " gill-helix," supported by the 

 dorsal segment of the fourth branchial arch, enclosed in a caecal extension of the 

 branchial cavity, and derives its blood from the fourth afferent branchial artery *. 



1. HETEROTIS NILOTICUS. 

 (Plate XV.) 



Sudis niloticus (Ehrenberg), Cuvier, Eegne Anim. 2nd ed. i. p. 328 (1829) ; Piippell, Besclir. n. 



Fiscbe Nil, p. 10, pi. iii. fig. 2 (1829). 

 Sudis adansonii, Cuvier, 1. c. 

 Garofche, Bifaud, Voy. Egypte, pi. cxc. (1830). 

 Ileterotis ehrenbergii ? Cuvier & Valenciennes, Hist. Poiss. xix. p. 469, pis. ccccclxxxiii. & ccccclxxxiv. 



(1846). 

 Ileterotis adansonii, Cuvier & Valenciennes, t. c. p. 478. 



Ileterotis ehrenbergii, Hyrtl, Denkschr. Ak. Wien, viii. 1854, p. 73, pis. i.-iii. 

 Ileterotis niloticus, Giinther, Cat. Fish. vii. p. 380 (1868), and Petherick's Trav. ii. p. 266 (1869) ; 



Steindachner, Sitzb. Ak. Wien, lxi. i. 1870, p. 565, pi. viii. fig. 2 ; Hemprich & Ehrenberg, 



Symb. Phys., Zool. pi. i., and Zoot. pis. viii. & ix. (1899) ; Budgett, Tr. Zool. Soc. xvi. 1901, 



p. 128, pi. xi. figs. 6 & 7. 



Depth of body three and a half to four and a half times in the total length, length 

 of head three and a half to four and three-fourths times. Head short and thick, 



* Of. Hyrtl, Denkschr. Ak. "Wien, viii. 1854, p. 85, pi. ii. fig. 2 & pi. iii. fig. 1. This paper deals with the 

 general anatomy of the fish. 



