346 THE FRESII-WATER FISHES OF EUROPE. 



beyond the mandible. The breadth of the frontal interspace between the eyes 

 is one and a third times the orbital diameter, and the distance of the hinder 

 edge of the operculum behind the orbit is twice the orbital diameter. The 

 fold of skin in front of the eye is fairly large, and the narrow pupil is 

 pointed towards it. The usual mucus-canal is developed behind and below the 

 eye. The maxillary bone extends back below the front margin of the orbit 

 and is one-fourth of the length of the head. The supplementary bone on the 

 maxillary is rather narrow. The tongue has five pointed curved teeth. There 

 are eight branchiostegal rays. The pseudobranchiaB are large, but the fringing 

 is short. The gill-rakers on the last branchial arch are fine, pointed, rather short, 

 and about nine in number. The frontal and dorsal profiles form a continuous 

 arch. 



The dorsal fin commences in front of the middle of the body; it is as 



Fig. 166. COREGONUS HIEMALIS (jURINE). 



long as the caudal. The ventral and pectoral fins are also equal ; and, as in 

 other species, the anal has the shortest rays. The adipose fin is broad and 

 blunt. The colour is always pale ; on the back it is brownish-yellow or grey. 

 The \ipper part of the head is yellowish- white, and the sides arid operculum are 

 silvery. The pectoral fins are colourless and transparent, but all the other fins 

 are bordered with black ; the iris is silvery. The flesh is firm and well-flavoured. 

 This fish spawns during September and October. It commonly lives in a 

 depth of about forty fathoms. When captured the body becomes distended 

 by the reduction of the atmospheric pressure on the gas in the air-bladder, 

 which is so inflated as often to burst the abdominal walls; and as the torn 

 condition is unsightly, the fish is but little caught. Sometimes, when 

 flying before a pursuing Pike, or otherwise rising to the surface attracted by 

 insects on the water, it falls back dead from the pressure of the expanded 

 air on the blood-vessels. 



