THE FLAT-FISHES 233 



its range includes the most northern parts of the Scandinavian 

 coast. 



The spawning-time is said to be in spring and summer — 

 a somewhat wide range. Mcintosh quotes Malm to the 

 effect that a nearly ripe egg measured just over 3^5- in., the 

 larva measuring about y^ in., and having yellow dots on 

 the fins. The egg has a single oil-globule, like the rest of 

 the present subdivision of flat-fish. The yellow on the fins 

 became deeper and extended to the head after a few days. 



The One-spotted Topknot (Z. unimaculatus) is rough on 

 the lower side as well as on the upper, a most uncommon 

 condition in flat-fish, and only familiar otherwise in some turbot 

 from Norwegian seas, in which the tubercles grow on both 

 the right and left sides. As further grounds of distinction 

 from the commoner species, we have the dark spot in the 

 middle of the coloured side, from which the present subject 

 takes its name, and also the greater length of the first ray 

 of the dorsal fin. There are also gaps in the marginal fins, 

 which is not the case in the common kind. 



The distribution is somewhat more southern, for the onc- 

 •spotted topknot occurs sparsely in the Mediterranean, but is 

 said to be absent from the most northern waters inhabited by 

 ■the other. Mention has already been made of the preference 

 which these topknots have for rocky ground, and of their 

 power of clinging to the surface of rocks. It may therefore 

 be, as Cunningham suggests, that this has placed them out of 

 danger of the trawl in many localities, where they are in 

 consequence less rare than commonly described. This is 

 a smaller topknot than the last, having been recorded to 

 .a length of no more than 5 in. 



The ripe egg, taken from a fish in 1892 (which was 

 not, however, fertilised), measured, in spirit, nearly ^ in. 

 On a subsequent occasion (1897) another ripe fish was 

 .taken at Teignmouth, and the eggs were in this case 

 hatched out in the Plymouth tanks. 



