1903-4.] Mr Calderwood on Bull Trout of Tay and Tweed. 35 
If we examine the Tweed bull trout, locally termed simply sea 
trout, as it comes from the sea at Berwick, its appearance is very 
different from that of the typical S. trutta. It is not a very 
silvery fish, and the sides are profusely spotted. This condition is 
constant in Tweed trout of all sizes. In examining a large 
number of these trout at Berwick last August, I was fortunate 
enough to find at the same time a single small specimen of the 
typical trutta , a fish of 2 J lbs. The brilliant sheen of this fish was 
very distinct from the rather faded grey appearance of the Tweed 
trout of the same size. The head had the conical appearance so char- 
acteristic of S. trutta — small in proportion to the length of the fish, 
with the maxillary bones well sunk into the surface, so as to give 
that smoothness and compact appearance which always seems to 
me a noticeable feature in typical examples of the species. The 
operculum and suboperculum united also in a rounded angle only 
slightly below the level of the eye. In the grey trout the head 
is flatter on the sides and the bones of the mouth more prominent, 
thus giving a coarser appearance to the head. The gill cover is 
more angular, and the angle is at a lower level, being in a line with, 
and sometimes even rather below, the level of the posterior 
extremity of the maxilla. On this account the lower margins of 
the suboperculum and interoperculum are straighter and more 
horizontal than in trutta or salar. A rather marked peculiarity of 
the preoperculum struck me, which does not appear to have been 
referred to by any of the authors whose works I have consulted. 
Instead of the posterior margin being gently curved or slightly 
sinuous, I found that the great majority of these fish have a 
crescent-shaped notch in the posterior margin of this bone. In 
a few cases two less distinct notches occurred, while in one or two 
examples three less deep notches were present, giving to the 
outline of this bone a rippling or undulatory appearance. In 
only one case out of the twelve or thirteen dozen fishes examined 
did I find no trace of indentations on the preopercular bones, 
while in one other case I found the bone of one side of the head 
with the usual deep single notch, while the bone of the other side 
of the head was unindented. 
