226 



Part III. — Sixteenth Annual Rei^ort 



young plenronectidse. But the larval and post-larval forms of the flat- 

 fish, with the exception of one or two well-marked stages in certain 

 forms, such as the lemon dab, have hitherto been simply classed together 

 as pleuronectids in the reports of the trawlings of the Garland ; it was 

 so difficult to distinguish the one from the other. Most of the specimens 

 collected by the GarlamVs officers, as well as those taken in St. Andrews 

 Bay and in the rock-pools, have been slowly accumulating during the 

 last thirteen years under the supervision of Professor M'Intosh. 



The presence of young flat-fish at the tidal margins has long been 

 known. In the "Researches," Professor M'Intosh considered that the 

 more completely metamorphosed specimens, aboat 14mm. in length, were 

 flounders, while the thinner, more transparent, and less metamorphosed 

 specimens at the same size might be plaice. Later, when the flounder 

 had become better known, and its characteristics at that size distin- 

 guished, he thought that these might be either plaice or dab. 



In the " Researches " also, Professor M'Intosh included under the long 

 rough dab certain specimens from 5mm. to 14mm. long, but without 

 giving drawings or detailed descriptions. 



In "A Treatise on the Common Sole" (1890) Mr. Cunningham gives 

 two drawings of the flounder in its transformation stages, and in the 

 "Journal of the Marine Biological Association"! he narrates that he 

 had obtained young plaice, dabs, and flounders, but does not give their 

 characteristics or distinguish them in their early stages from 10 to 15 mm. 

 The pelagic forms — when the young flat-fish are in their post-larval or 

 transformation stages — have been obtained and described by several 

 observers. 



Dr. Petersen, in the Report of the Danish Biological Station" (1893), 

 gave a brief outline of the young flat-fish of Danish waters. Without 

 going into detail he clearly marked off" the relative positions of the plaice, 

 dab, and flounder, stating the sizes at which each completed metamor- 

 phosis. These were — about 8 mm. for the flounder, 10 to 11 mm. for the 

 plaice, and 12 to 13mm. for the dab. Betv/een " 12 to 13 mm. the plaice 

 is very like the common dab," but "is distinguished from the latter by its 

 small eyes (the diameter of the apple of the eye is only half the length 

 of that in the average-sized common dab) and by a different pigmenting." 

 He gives a drawing of a young pelagic stage of the long rough dab, which 

 seems to have been about 18 to 20 mm. long, and states the character- 

 istics — " particularly projecting stomach region, and the concave profile of 

 their heads." 



Mr. Holt, in his report on the Irish survey {loc. cit.\ minutely 

 describes the characteristics of certain specimens considered to be plaice, 

 dab, and long rough dab. A complete series of the plaice was obtained, 

 and he gives drawings of five specimens from 10mm. to 21mm. The 

 specimens of the dab were from 12'25mm. to 16mm., but none below 

 12*25mm. were obtained, nor from 16mm. to the stage when the adult 

 characteristics are assumed. It was therefore by a process of elimination — 

 comparing the specimens with those of the plaice on the one hand and 

 those of the long rough dab on the other — that these forms were called 

 dabs. The general diff'erences between the plaice and the dab are : — - 



At the same total length (1) the rotation of the eyes is less complete 

 in the dab than in the plaice. 



(2) The height of the body is relatively greater [in the plaice than in 



the dab. 



(3) The size of the eye, as compared with that of the head, is larger 



in the dab than in the plaice. 



(4) A general pigmentation of the ocular side is assumed by the 

 young plaice at a smaller size than in the case of the young dab. 



* Loc. cit. 

 t Loc. cit. 



