of the Fishery Board for Scotland. 



235 



under natural conditions may not be so great or may be greater, but 

 since the conclusions have been based on such a large number of 

 specimens these limits should be fairly representative. Since these 

 results are for spirit specimens, the results of Ehrenbaum and Dannevig 

 for living specimens have been compared with them. (1) Below 9mm. 

 the plaice is distinguished by its proximity to the larval condition. (2) 

 Between 9mm. and 10mm. the two forms are very much alike, the dab 

 being, if anything, rounder in head and body. (3) Between 10mm. and 

 13mm. the plaice is distinguished by its earlier metamorphosis, greater 

 breadth, and, to a certain degree, by greater amount of pigmentation. 

 (4) Above 15mm. the plaice is distinguished by these same characteristics, 

 and by the gradual assumption of adult features. Between 13mm. and 

 15mm. these distinctions hold for the majority of forms, but there are 

 specimens in the collection about which there is some doubt, due to the 

 late assumption of complete metamorphosis by some of the specimens of 

 the plaice, and the early assumption of this stage by some specimens of 

 the dab. This difficulty, which will be between 14mm. and 16mm., 

 may not exist for living specimens, because contraction by spirit will 

 affect the dab at this stage more than the plaice. When metamorphosis 

 is half complete, or about this stage, there is a bend in the dorsal fin, close 

 to the left eye, in the plaice which is not present in the dab. 



Definite measurements are given in the Table of Characteristics. 



Long Rough Dab. 



The eggs of this form occur with those of the plaice, and are common 

 in the months of March- and April, both on the east and west coast of 

 Scotland. A large number of specimens are present in the collection, 

 which, from their occurrence with the plaice and dab in such numbers, 

 are most likely to be long rough dabs. In size they range from 4mm. to 

 21mm. ; from the larval condition to when the left eye has begun its 

 migration but is not yet half-way. These later post-larval specimens 

 agree with the drawing of Dr. Petersen. This observer does not mention 

 the size of the specimen, but, judging from those in the collection, it 

 would be from 18mm. to 20mm. long, though it may have been smaller, 

 since the other flat-fishes ot" Danish waters undergo metamorphosis sooner 

 than those of British. With the exception of some doubtful damaged 

 ones, all the specimens ascribed to this species are very distinct from those 

 of the other species, and possess the characteristics given by Dr. Petersen 

 ' — " particularly projecting stomach region and the concave profile of 

 their heads." 



The specimens described by Mr. Holt differ from these in many respects. 

 His smaller specimens, from 8*7mm. to 12 •25mm., which are divided 

 into two series, seem to be of this species, the difference in the degree of 

 transformation being quite within the limits of variation, which is 

 considerable in these forms, as shown by the plaice and the dab. There 

 are several important differences in these from those of the North Sea. 

 As Mr. Holt remarked, the concave profile of the head is hardly evident 

 in his specimens, nor is the projecting stomach region; development is 

 further forward also. 



What is so noticeable in the specimens from the North Sea is the 

 peculiar manner in which the fin-rays appear. Their first appearance, 

 between 9mm. and 10mm. — this is in agreement with Holt — is half-way 

 along the dorsal and ventral fins. Between 10mm. and 14mm. they 

 increase forwards to the head and backwards to the tail. This is not 



