206 THE FRESH- WATER FISHES OF EUROPE. 



HYBRID BETWEEN CHONDROSTOMA POLYLEPIS AND LEUCISCUS 



ARCASII. 



Steindachner found the fish which he thus accounts for as a hybrid in the 

 River Tara, a tributary of the Douro, in the north of Spain. In form, pharyn- 

 geal teeth, and bony covering of the lower jaw, it agrees with Ch. polylepis, 

 but the mouth is semicircularly curved as in Leuciscus arcasii. The snout is 

 not so prolonged as in the former. The dorsal fin is variable ; in some speci- 

 mens it is like Leuciscus arcasii in having seven jointed rays, and a convex 

 upper margin ; others are like Ch. polylepis in having eight jointed rays and 

 a concave upper margin to the fin. The jointed rays of the anal fin vary from 

 seven to nine. The number of scales in the lateral line is not constant ; one 

 specimen agrees with Ch. polylepis in having sixty-two scales, while the others 

 are intermediate between fifty-two and fifty-nine, and resemble L. arcasii 

 in the character of the scaling. The scales are larger than in Ch. polylepis 

 with strong concentric striping and a fan of ten to sixteen rays. There 

 are eight and a half to nine and a half rows of scales above the lateral line, 

 and four to five rows below. In the example with sixty-two scales in the 

 lateral line, there are eleven rows above it. The colour is the same as in 

 Lenciscus arcasii ; a dark blue-grey back, longitudinal bands above and along 

 the lateral line, and orange-yellow bases to the fins. 



