254, EXPERIMENTS AND OBSERVATIONS. 
relative of Zeugopterus is certainly the megrim, which has the per- 
foration in the gill-septum. This fish was united with Zeugopterus 
by Steenstrup, with Arnoglossus by Day. Giinther places it as a 
sub-genus of Rhombus, with the name Lepidorhombus, and in my 
opinion it is best to separate it altogether under this name. The 
only other species of the genus is Lepidorhombus Boscwt. 1 do not 
know whether the latter has a perforated gill-septum, but think it 
probable. The chief characters of Lepidorhombus are the very 
large mouth, thin body, and skin with little pigment and ciliated 
deciduous scales. Ottharus linguatula, Ginther, closely resembles 
the megrim, but has unequal teeth, and is destitute of the perfora- 
tion of the gill-septum, Arnoglossus is a fairly well-marked genus, 
of which several species have been described, but only two (laterna 
and Grohmanni) are definitely known to myself. The scales are 
small and feebly ciliated, very deciduous, the skin also being very 
thin and weak, so that it is easily torn and detached. The mouth 
is comparatively small, much smaller than in Lepidorhombus. The 
fish are of somewhat small size. The presence of secondary sexual 
characters must be regarded as characteristic of this genus, some of 
the anterior median fin-rays being elongated in the male. All these 
forms are confined to the coast of Hurope. ‘Two species from deep 
water in the Gulf of Mexico have been assigned to Arnoglossus, but 
there is little probability that they rightly belong to 1. 
Rhombus is a genus which is distinct from all those above 
mentioned, It has a broad, usually strong body, with a thick skin ; 
a broad interorbital area, whereas in the preceding forms it 1s narrow, 
and scales small, cycloid, or wanting. The mouth is large and the 
jaws strong ; the teeth small, in bands, and nearly equal. The specific 
differences consist chiefly in the character of the dermal armature. 
In the brill (Rhombus levis) the scales are cycloid and imbricate on 
both sides of the body, and there are no bony tubercles; the 
anterior rays of the dorsal are somewhat prolonged and much 
branched. In the turbot (Rhombus maximus) there are no scales, 
but bony tubercles scattered over the upper surface, absent on the 
lower; and the anterior dorsal rays are not prolonged, or distin- 
guished in any way. These two are confined to Europe; on the 
American coast of the Atlantic there is a species resembling the 
brill called R. maculatus, known commonly as the window-pane, from 
its thinness. It is scaled on both sides, and the anterior rays are 
more prolonged than in the European brill. Transitional forms 
between the brill and the turbot have long been known, and were 
originally described as a separate species under the name R. meoticus 
by Pallas in Zoogr, Ross. As. in 1811. Specimens from the Black 
Sea have been frequently described since, and they seem to be more 
