Arthur. — On the Brown Trout introduced into Otago. 503 



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 41bs. 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 

 j 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. Gimther calls a "lower limb," gener- 

 ally very pronounced in outline, and with three or 

 more strife on the surface of the bone. The suboper- 

 culum 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 

 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 

 yet seen by me ; although one other trout I have ex- 

 amined had nearly the same form of this bone. But 

 fig. 3 is a very common shape in the old male trout. 

 There is sometimes, but not often, a slight difference in 

 S outline between the subopercles on either side of the 

 I head in the same fish. In young examples the margins 

 of the opercula are rounded and graceful, but in old fish 



* In such specimens the head is small like a female, and no development of either 

 melt or roe of a decided character. 



