4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



(2) Alestes group, including Alestcs, Micralestcs, and Pciersiiis, in whicli the 



radii are few but very strong, the sculpture is often weak in the apical 

 region, and the scales are frequently much broader than long. 



(3) Ilydrocyon group, in which the apical field is more or less rugose, and the 



radii are evanescent, the basal radii usually absent. The dorsal scales 

 of Hydrocyon show numerous but very weak apical radii, which pro- 

 duce some crenulation of the very thin margin, indicating a slight 

 approach to a ctenoid condition. H. forskalii examined. 



It appears probable that Sarcodaces odoc (River Benue, north of Ibi, H. L. 

 N. Traill) has the more primitive type of scale. Hydrocyon forskalii (River 

 Nile) can be derived from this by the general weakening of all the structures; 

 while the Alestes group represents a reduction of the radial system, with a 

 much stronger development of what remains. Thus three fairly distinct tribes 

 would appear to be indicated : Sarcodacini, Alestini, and Hydrocyonini, their 

 typical genera Sarcodaces, Alestes, and Hydrocyon respectively. The term 

 Hydrocyonini was used by Bonaparte as early as 1838 (Nuovi Annali delle 

 Sci. Nat. 2, p. 132). BryconcEthiops I have not seen. 



Alestes 



Group A. Scales very large, the transverse diameter over 15 mm. 



(i) Scales very much broader than long. 

 Alestes tceniurus Giinther. Kribi River, Cameroon (G. L. Bates). 



Scale about 10.5 mm. long and 16.5 broad ; basal radii about 12 ; discal 



region divided into many polygonal areas. 

 (2) Scales not much broader than long. 

 Alestes rhodopleura Boulenger. Mtondwe Bay, Lake Tanganyika (CMnningf on). 

 Scale about 18 mm. long and 21 broad; basal radii two; lateral radii two 

 on each side, more or less inclined to be divided or delta-like mar- 

 ginally; apical radii few and quite irregular; apical region rugose; 

 circuli of basal region extremely fine. 

 Alestes macrolepidotus Cuvier and Valenciennes. River Nile. Structure 

 essentially as in A. rhodopleura; rugosity of apical region, resulting 

 from modified circuli, very pronounced. The discal region may be 

 reticulate. 



Group B. Scales smaller, the transverse diameter much less than 15 mm. 



Owing to individual variation and the small amount of material available 

 it is impossible to determine the precise specific characters in this 

 group. Some of the species probably cannot be separated on the 

 scales. In no case are the scales of the very broad tcsniurus type. 

 (i) Comparatively large reddish scales, with the apical rugosity poorly 

 developed. 

 Alestes macro phthalmiis Giinther. Lake Tanganyika (/. E. S. Moore). 



Radii very few and feeble, in the sing"le scale examined there is only one 

 basal ; scale about 7.5 mm. long and 9 broad. 

 Alestes liebrechfsii Boulenger. Coquilhatville, Upper Congo (Delhes). 



Radii more numerous, about six basal, but two of these incomplete ; discal 

 region with some polygonal areas ; scale about 8.5 mm. long and 

 10.5 broad. The characters separating these two are doubtless 

 variable. 



