MADE AT THE PLYMOUTH LABORATORY. 255 
abundant there than elsewhere. Steindachner (Ichth. Berichte, 
1868) states that a complete series of gradations between the 
ordinary turbot, in which the scales are obsolete, and the scaly 
turbot, which is more or less completely scaly, is to be observed. He 
obtained one of the most completely scaled specimens from the 
Baltic. Whether these specimens are to be regarded as variations, 
a variety, or as hybrids, we do not know. If they breed true, so 
that a scaled specimen is derived from scaly parents, then they 
form a variety, but this seems unlikely ; it seems more probable that 
scaled forms occasionally develop from ordinary parents. 
Another interesting genus in the Rhombine closely allied to 
Rhombus is Rhomboidichthys, called Platophrys by Jordan and Goss. 
In this genus the scales are small and ctenoid, and not deciduous. 
The interorbital space is very broad, and the peculiar position of 
the dorsal eye gives a curious appearance to the fish. There is a 
slight difference between the sexes, the pectoral of the left or upper 
side being filamentous in the male. Many species have been 
described from the West Indies and east coast of South America, 
and one from the Pacific coast. 
It is unnecessary at present to refer to any of the remaining 
genera or species of the Rhombinz which are less known. The 
principal characters by which the best known forms are distinguished 
have been mentioned, and what do we know of the functions of those 
characters ? No one has hitherto been able to suggest a reason why 
the scales are more useful to the brill and tubercles to the turbot. 
We do not know why the male Arnoglossus requires elongated fin- 
rays, a kind of piscine moustache, a masculine ornament which is 
developed in several other species of fish. We can say with truth 
that the Rhombinze are for the most part predaceous flat fishes 
which seize active prey, and to this habit of life the large sym- 
metrically developed mouth and teeth are adapted. It is quite 
possible, too, that if we knew the habits of particular species more 
exactly and more completely, we should see that the whole muscular 
system and shape of body, as well as the particular size of mouth, 
were adapted to the particular habits and surroundings. But this 
leaves some of the features most important in diagnosis, such as 
the scales and the secondary sexual characters, unexplained. 
A different set of characters offering similar difficulties occurs in 
the sub-family Pleuronectine. ‘The common features of this sub- 
family as diagnosed by Jordan and Goss are the following : 
Mouth small, asymmetrical, the jaws on the eyed side with nearly 
straight outline, the bones on the blind side strongly curved ; den- 
tition chiefly developed on the blind side; eyes large; edge of 
pre-opercular not hidden by the scales ; pectoral fins well developed ; 
