238 



THE FRESH- WATER FISHKS <>F 



horizontal. The dorsal fin commences in front of the middle of the length. It 

 is placed between the ventral and anal fins, is much higher than long, and 

 truncated posteriorly. Its longest ray is twice the length of the shortest. 



The base of the anal fin is as long as the head; its border is slightly concave; 

 the last ray is half the length of the longest. Though the ventral has ils 

 longest rays equal to those of the dorsal, it does not reach the vent. The 

 pectoral fins do not reach the ventrals.; the caudal fin is evenly lobed. The 

 anterior anal rays commence behind the last dorsal rays. 



The largest scales -are on the lateral line, but measure less than half the 

 diameter of the eye. The smallest scales are on the breast and anterior part 



Fig. 135. ALBUKNUS MENTO (AGASSIz) . 



of the abdomen. They are marked with many radiating rays and thick con- 

 centric lines, have a pale silver lustre, are soft, and easily fall off. 



There is a spur-like scale extending on the base of the ventral fin, which in 

 old age becomes as long as the fin. 



The cephalic canals extend on the sub-orbital ring, and to the nasal aper- 

 tures, and are especially developed on the pre-operculum. 



The colour of the head and back varies from dark green to steel-blue ; the 

 sides are pure silver. 



All the fins are grey and transparent, but the dorsal and caudal fins are 

 marked with black spots. The iris is silvery, sometimes spotted with black. 



This is the largest species of the genus, and reaches a length of ten inches, 

 though Bavarian specimens are rather larger than those from Austrian 

 waters. It frequents mountain streams, and streams which flow into moun- 

 tain lakes, preferring clear cold water with a stony bottom. It often lies 

 for a long time perfectly still against the stream, like a Trout, and then moves 

 with astonishing speed. It is rare in the Danube, but is found in the Atter 

 See, Traun See, Grmundner See, in Austria; the Ammer See, Chiem See, and 



