Artuur.—On the Brown Trout introduced into Otago. 508 
The form of the head, body, and tail fin is subject to considerable modi- 
fications. In females, more particularly adults, the head is smaller and finer 
in shape than in males. In females the head is usually in adults one-fifth 
of total length, and in males, one-third to one-fourth, among my specimens. 
It is very difficult in young trout up to half a pound in weight, to tell the 
sex from the head and spots. Even dissection sometimes has shown me no 
sexual development sufficient to determine the question. But usually, in 
trout from half a pound upwards, it may be seen from the size of the head, 
form of mandible, and presence or absence of red spots. The male is most 
commonly to be recognized by its large head and fins, the hook on the lower 
jaw, and the red spots on its body. In one or two rare examples I have 
found a male of 21bs. to 4lbs. with very little of a hook at all, while I have 
seen a female of similar size with quite as large a hook on its mandible. 
These cases are, however, very exceptional among Otago trout.* The 
form of the maxillary is not very constant, being broad 
and fine or coarse, narrow and fine or coarse, always 
however, in adults having its posterior end in line of, 
or behind line of, a vertical from posterior margin of 
orbit. The opercula seem inconstant in shape within 
certain limits. The preoperculum in our trout has 
always, contrary to his description of non-migratory 
trout, what Dr. Günther calls a ** lower limb," gener- 
ally very pronounced in outline, and with three or 
more strie on the surface of the bone. The suboper- 
Bculum of our Otago trout is generally of a trapezoidal 
form, as in fig. 1 in the attached woodcut, with the 
exterior angle more or less circular, or it might be called 
Ma roughly rectangular. Fig. 2 is a case of a young 
female trout from the Waipahi, in which the rectangular 
form is very decided. It approaches nearer to Mr. 
Yarrell’s typical form (fig. 4) than in any other trout 
il yet seen by me; although one other trout I have ex- 
amined had nearly the same form of this bone. But 
fig. 8 is a very common shape in the old male trout. 
There is sometimes, but not often, a slight difference in 
outline between the subopercles on either side of the 
head in the same fish. In young examples the margins 
of the opercula are rounded and graceful, but in old fish 
ide s iii sale 
* In such specimens the head is small like a female, and no development of either 
melt or roe of a decided character. 
