16 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XII. 



and eye, i.i in interorbital width. Dorsal I, 5 ; base of adipose dorsal, 1.9 

 in interdorsal space; anal with 3 simple and 7 branched rays, its basal 

 length a little shorter than either the height of the anal or the length of 

 the adipose fin; pectoral spine in head, 1.4 (left side) or 1.6 (right) ; pelvic 

 fin extending a little beyond the anal origin, its length, 2.35; caudal fin 

 deeply forked, the upper lobe (measured from base of developed rays) 

 1.2 in the lower lobe, which is contained 1.2 times in the head. Colora- 

 tion as described and figured for C, deckenii. 



Tilapia athiensis Boulenger. 



Tilapia nilotica athiensis Boulenger, Proc. Zool. Soc. London, 1916, 



P- 345- 



Dr. Boulenger recently presented an interesting account of the 

 variation, among Cichlids, of the number of spines in the anal fin. He 

 described, as Tilapia nilotica athiensis, certain specimens from the Athi 

 River system, which differ from Tilapia nilotica only in the constantly 

 increased number of anal spines (4 or 5 instead of 3) . While accepting 

 Boulenger's general conclusions, we consider that the Athi form should 

 be given full specific status. A single genetic character, constant in all 

 or in the large majority of each of two non-intergrading forms, is re- 

 garded by us as sufficient grounds for specific distinction. 



