230 



Part III. — Sixteenth Annual Report 



the difference is of specific value. This condition, the dorsal fin over- 

 hanging the eye, is present in the lemon dab, perhaps also in the long 

 rough dab. When the bending occurred (due to the twisting of the 

 forepart of the skull) the eye was considered half-way, when the pupil 

 was in a line with the fin a little distance from the eye. 

 The following curve represents the result : — 



to. 



/6 



A/ 

 // 

 /o 



S 



6 



1 



















































7 



























1 























n 



1 1 

















\ 







L ' 















\ ; 





I 

























\ : 



\ 1 

 1 / 

 < 1 















X 







\l 

 X 







^ /o // /A /J // 



There are several considerations that prevent me from thinking this curve 

 accurate, but since it fairly well represents the tendency of the rest of the 

 specimens to fall into two groups, as well as the point where they over- 

 lap one another, it is quite definite. The lower is taken to represent the 

 plaice, with a maximum for this stage at 12mm.; the higher group, the 

 dab, with a maximum at 15mm. Between 13mm. to 13 5mm. is the 

 position where there is difficulty in separating the specimens at this stage. 



It might be thought that the lower group should represent the dab, the 

 higher the plaice; but there are no specimens to support this view. 



It may also be thought that the curve only represents one species, the 

 plaice, and that the small number of specimens accounts for the minimum 

 about 13*5mm. Apart from the fact that a series of specimens represent- 

 ing the upper group (figs. 1 to 13) differs in characteristics from a series 

 representing the lower group (such as that given by Mr. Holt), from 10 

 to 16'5mm. is too great a variation to ascribe to one species at this stage. 

 The presence of two species seems certain from this alone. 



All specimens below 13mm., with metamorphosis half complete or more 

 than half complete, were separated as plaice, and all above 13 5 mm., with 

 the eye not half-way, were considered to be dabs. This separation was 

 found to agree with the general distinctions made by Mr. Holt, viz., at 

 any length the breadth of plaice was greater than that of dab, metamor- 

 phosis was further advanced, and for most there was more pigment on the 

 plaice than on the dab. 



