26 



type, as t sliall here ciill tliem, have afterwards alwaj's beeii easy to recog- 

 nise; but to decide to wliich species one belongs, and to which tbe other, 

 within the genus Zeugopterus, has hitlierto caused great diffieulties. 



The genus Zengopterus, in my opinion, iuchides the 5 species: uni- 

 maciilntus, pmictatiis, norregiais, mega^toma, and lioscri. In all these five the 

 isthmus between the gill cavities is peii'orated. Holf himself was in doubt 

 to which of the two firstnamed species the smooth ones belonged; but he 

 thought that the whole form of their body necessarily referred thera to one 

 of these two. With some doubt he then referred them to /. uiriniaciihitus, 

 because his oldest speciinen had more than 80 dorsal rays and more tban 

 60 anal rays, and this number agreed best with the information he had 

 found in literature with respect to Z imimacidafus. As for the spiny young 

 ones, then he hesitated between Bhomhus lævis and Zeiigopterns norrpgiciis. 

 The number of fin-rays, c. 80 dorsal raj's and c. 60 anal rays might verj' 

 well refer them to the latter. The young ones of Bhomhus Icevis have been 

 described afterwards by others, also by myself in "Report IV; to compare 

 these spiny young fish with them is (|uite out of the question. 



In "J. M. B. A." (N. S.), vol. III, 1893—95, p. 202—205, J. T. Cun- 

 ningham describes some spiny young sinistral flatfish, from Plymouth, 

 which very nearly agree with those described l)y Holt. The_y have 

 as raauy as 90 dorsal rays and 69 anal rays, and in his opinion, 

 therefore, their parents cannot be Z. norvegicns. He refers them to Z. 

 pundatus, which has a larger number of fin-rays. Of the smooth young 

 flatfish he gives no particulars. 



M'Infosh has on various occasions described and mentioned young flat- 

 fishes, both of the smooth and of the spiny type. In his last work, "British 

 Marine Food-Fishes", 1897, he comes to the result that the smooth forms 

 belong to Z. punctatus, the spiny ones to Z norvegicus. One of his argu- 

 ments is that Z. unimacnldfits has not been fonnd on the eastern shores of 

 Scotlaud; another, and a more essential one perhaps, is, that he has found 

 that the dorsal tin of the smooth type may number as many as 89 rays 

 and the anal fin as many as 64 ("10. Ann. Report F. B. for Scotland", 

 1891, p. 277). In this respect, consequently, he meets the same difficulties 

 by referring the thorny tj'pe, with 90 and 69 rays, to Z. norvegicns, as b}' 

 referring the smooth one to the same. He is freer, therefore, in his choice 

 between Z. norvegicus and Z. pimctatus than Holt is, and tiierefore refers 

 the smooth young ones to the latter, which, in his opinion, they resemble 

 most in the form of the body, and the spiny ones to Z. norvegicus 

 which is more like these. Holt, at first, also thought this to be the correct 

 determination of the spiny young ones. Z. ■imimariildtiis is considered by 

 M'Intosh to be excluded, because, as above mentioned, it has not been 

 found on the eastern shores of Scotland. 



In "J. M. B. A." (N. S.), vol V, 1897—99, p. 12S — 135, however, Holt 

 again discusses tiiis ([uestion, and is of opinion that Cimninglimtt has proved 



