NATURAL HISTORY. 
77 
The shad^ Clupea alosa, is another fish which the 
Severn affords in great perfection. These fish gene- 
rally appear in May, though sometimes in April ; 
this however depends a good deal upon the quality 
of the water ; if it is clear^ they ascend early in the 
spring, but if there happens to be a flood, they wait 
till the waters are restored to their former purity, 
and if they meet with a flood in their progress 
upward, they immediately return, and keep below 
Gloucester. The weight of the shad is seldom less 
than four pounds ; they continue in the river about 
two months, and are succeeded by a variety called the 
twaite, which is less than the shad, never weighing 
more than two pounds, and is but little esteemed. 
Dr. Fleming says that the celebrated white-bait of 
the Thames, which appears near Blackwall and 
Greenwich during the month of July, is the fry 
of this fish; but as although the shad are plentiful 
in the Severn, we hear nothing of the white-bait, 
further investigation seems to be required on this 
point. 
It is a curious circumstance that though the salmon 
ascend many other tributaries of the Severn, and are 
frequently caught in the Teme, yet neither that fish, 
nor the shad, lamprey, nor lampern, ever attempt to 
enter the Avon at Tewkesbury, which joins the 
Severn at that place. There are certainly various 
impediments to the passage in mills and weirs, but 
such obstacles are in other places surmounted by 
salmon. It is, however, stated by the fishermen, that 
the salmon manifest the utmost aversion to the Avon 
