THE SHADS, THE EELS, AND THE LAMPREYS 289 
of common origin. Scarcely could two fish be more different 
in appearance, but if there is anything more slippery than fish 
themselves, it is the nomenclature by which men have dis- 
tinguished them at different times. Anyhow, the shad was 
known in Anglo-Saxon as sceadda, which appears to be the 
same word as the Gaelic sgadan and the Welsh ysgadan, 
herring, and the shad is but a larger herring. 
The shad is remarkable as being the only British fish of 
fresh water that possesses eyelids. These are merely folds 
of transparent skin, opening with a vertical slit, instead of a 
horizontal one, as in birds and mammals. The body is 
covered with large silvery scales ; there is a conspicuous and 
large dark blotch on the shoulder just behind the operculum, 
or upper gill-cover ; sometimes followed by two or three 
other such spots in a horizontal line. The abdomen forms 
a sharp ventral edge from the anal fin forwards, armed with 
a row of from thirty-seven to forty-two spinous scales, like 
the teeth of a saw, supported by the sternal ribs. The most 
conspicuous of the fins is the caudal, which is deeply cleft, 
with sharply-pointed lobes. The middle rays of this fin are 
covered with a peculiar arrangement of long, pen-like scales, 
upon each of which are fixed three or four smaller scales. All 
of the Herring Family are distinguished by the ample 
development of the gills, the gill-opening being very large. 
In the Allis shad the gill-rakers (Fig. III. 62, p. 23) form a 
remarkable feature, being very long and fine, and numbering 
from sixty to eighty. 
The shad is a well-known visitant to most of the large 
rivers of Western Europe and the Mediterranean. It is also 
found in the Danube, but in Russia its place is 
supplied by a kindred species, the Black Sea herring 
(Clupea pontica). It used to be common in the Thames, and 
still frequents the Severn and the Wye. The principal shad- 
fishery is at Newnham, near Gloucester, where operations are 
begun towards the end of April or beginning of May, when 
ug 
Distribution. 
