132 BRITISH FRESHWATER FISHES 



greatest depth, usually about one-fourth of the 

 length to the base of the caudal fin, but in large 

 specimens sometimes nearly one-third, is not far 

 behind the head ; the snout is blunt and rather 

 short, the eye of moderate size, protected by a 

 transparent lid with a vertical elliptical aperture 

 above the pupil ; the mouth is terminal and oblique, 

 with the teeth minute or absent and the maxillary 

 extending a little beyond the eye in the adult fish. 

 The gill-openings are wide and the gill-rakers are 



a. Ir 



Fig. 17. — Anterior branchial arches of Allis Shad (a) and Twaite Shad {b)^ 

 showing the difference in number and length of the gill-rakers. 



slender, very long, and in the adult fish very 

 numerous ; in specimens from i to 2 feet long I 

 count seventy-two to eighty on the lower limb of 

 the anterior branchial arch, and in one of 8 inches 

 sixty ; in smaller examples the number is still less. 

 The scales are irregular and deciduous and, therefore, 

 not very easy to enumerate ; I count seventy-two 

 to eighty-six in a longitudinal and twenty-one to 

 twenty-five in a transverse series ; the trenchant 

 ventral edge of the body is serrated, bearing a series 

 of bony scutes with backwardly directed points. 



