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Part III. — Sixteenth Annual Report 



remarked by Holt. From 12mm. to 17mm. there is very little change 

 in the degree of transformation, though variations are numerous, and in 

 one or two the left eye has begun to migrate before 15mm. 



The fin-ravs increase from the small numbers given by Holt — D. 

 67-70, A. 54-58, to D. 77-82, A. 58-61. 



The fact that the fin-rays are just appearing between 8mm. and 10mm. 

 together with the elongated form, the pointed appearance of the head, the 

 large mouth and mandible, and the amount of pigment along the myomeres, 

 leads one to think all these figures of Holt already mentioned as of this 

 species. The various stages in development appear sooner, however. In his 

 shorter series, which are not so like the long rough dabs of the North Sea as 

 the elongated series, the notochord does not prvoject beyond the hypural 

 structure at 9*37mm. ; in the specimens from the JJ^'orth Sea it is seen at 

 16mm. in some. In the largest specimens from the North Sea, 21mm., 

 the left eye is not yet half-way. There are no specimens later than this, 

 but, judging from these, metamorphosis cannot be complete until nearly 

 30mm. Mr. Holt shows a specimen at 27mm., metamorphosis com- 

 plete. Otherwise the specimens from the North Sea are in series with 

 this specimen, the largest being 6*7mm. broad where this is 8mm. 



Mr. Holt has filled up the gap between 12-25mm. and 27mm. by two 

 specimens which closely resemble the dab of the North Sea. The 

 distinctions between the two species at 13 to 15mm. in length are given as 

 " the larger mouth in the long rough dab." This, however, is not so 

 evident as in the smaller specimens at 9 to 11mm. "The asymmetry of 

 the head is more advanced in the common dab than in the long rough 

 dab" — but if fig. 102 (long rough dab), 13*87mm., be compared with 

 fig. 114 (common dab), 14*5mm., there seems little ground for doubt 

 that the two are of the one species. It was because he mistook the 

 variations of the plaice for dabs that Mr. Holt has considered the common 

 dab as the long rough dab. Another difference mentioned is the presence 

 of pigment along the lines of the myomeres, but, from what has been 

 said before, this is not altogether diagnostic, and is present in the 

 common dab. 



Fig. 103, length of specimen 14*77mm., described by Mr. Holt, had a 

 fin-ray formula of D. 80, A. 62. This certainly is beyond the limits of 

 the common dab, but in all other characters, breadth 4*75 to 4"87mm., 

 length of caudal fin, 2*6 to 2'7mm., degree of metamorphosis, they are like 

 the dabs of the North Sea. On the other hand, they are very different 

 from the specimens of the long-rough dab. The drawings and the 

 characteristics given in the Tables sufficiently describe the young post- 

 larval stages of this species, so that no further explanation is needed here. ' 



The Lemon Dab and the Flounder. 



It is unnecessary to refer to the characteristics of these forms in any 

 detail, they have been so clearly defined by the writer already quoted. 

 The distinguishing characteristics are drawn up, from personal observa- 

 tions, in the following Table. 



In connection with the lemon dab, it has to be mentioned that contrac-^ 

 tion, due to spirit, is very considerable during the early stages. Thus, 

 some specimens at 9mm. in length were found to have the fin-rays 

 developed, whereas some over 10mm. had no trace of them. Again, 

 specimens at 16mm. had the eye half-way, and various others from that 

 size to 25mm. were in the same stage. In all cases where contraction 

 is great it is easily detected by the folds of the fins. This was also 

 noticeable in many specimens of the long rough dab. 



