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These numbers of rays are, as it will "be seen, pretty well distinguished in 

 plaice and flounders (particularly in the anal fin) ; on the other hand they are nearly 

 always identical in common dabs and plaice. — The number of rays in the caudal 

 fin will only now and then help us out of that difficulty, as the plaice has here 

 18, 19, 20, 21, the flounder 16, 17, 18, and the common dab generally 18. There 

 are, however, exceptions from this rule. 



It seems as if the full number of rays is formed immediately in the begin- 

 ning of the bottom stage ; I have made no countings, however, to see if not a few 

 rays are added afterwards. But it cannot be denied that there is some difference in. 

 the number of rays in the dorsal as well as in the anal fin of the plaice in the northern 

 < 'attegat, compared to those in the southern at Grenaa and. at the northern, parts of the 

 Great Belt. 



In 39 plaice, not over 19 mm in length, from Frederikshavn, the average 

 number in the dorsal fin was 68, in the anal fin 53. Only one had 49 in the anal 

 iin, all others higher numbers. Only one had 65 in the dorsal fin, all others 

 higher numbers. 



In 15 plaice from. Samso, 3 under 20 mm , 12 over 20 mm in length, the 

 average number in the dorsal fin was only 67, in the anal fin 49. 9 had 47 and 

 48 in the anal fin, 1 had 49, the remainder more than 50. 4 had under 65 in 

 the dorsal fin, 10 more than that. 



I shall not go further into these enumerations, which must be carried out 

 on a greater scale at some future period in order to further elucidate this matter, 

 which is, I suppose, connected with the occurrence of the various races of plaice, 

 whose sizes I have mentioned in an earlier part of this report. — I should scarcely 

 have seen, on this occasion, that my countings suggested the above stated facts, 

 had not Georg Duncker in Kiel, written to me about his researches of the plaice in 

 the Baltic Sea — for which I thank him, hoping soon to see some further infor- 

 mation on the matter. 



The number of rays in the flounder does not show any difference in the 

 various seas — though a great many have been counted — nor might this reason- 

 ably be expected, as this fish does not, like the plaice, show any distinguishable 

 decrease in its length in the more inshore waters. 



The fry of the two species of Pleuronectes here mentioned can never, after 

 the pelagic stage, be mistaken for that of our other species of Pleuronectes: PI. 

 microcephalics and PI. cijnoglossus, the number of raj^s in the dorsal and anal fins of 

 these being exceedingly great. In the former the dorsal fin has c. 92, in the 

 latter as many as 111 — 117 rays. (See the figures, plate II, fig. 13, 14, as also the 

 pictures of PI. cynoglossiis in M'Intosh and Prince's great work, plate XVIII, fig. 7 — 9). 

 It might be thought, perhaps, that another of our flat-fishes, the long rough dab 

 (Hippoglossoides platessoid.es) , might rather be mistaken for a species of Pleuro- 

 nectes, but it is most nearly related to the large-mouthed flat-fishes. (See however 

 Mtrfm's mistake in his"».Fawwa« p. 510, and his earlier paper on this subject). 



It seems as if the plaice is not the only flat-fish which occurs in local or 

 geographical races (varieties), nor does the number of rays appear to lie the only 



