284 DR. TRAQUAIR ON THE ASYMMETRY OF THE PLEURONECTIDZÆ. 
In Plate XXXT. fig. 1, are represented the superficial Tace-bones on the eyed side of a 
Halibut; in fig. 2, those of the eyeless. On the ocular side observe the suborbital range 
(#'), extending along in direct relation to its eye (the lower one); but with this pecu. 
liarity, that the anterior suborbital bone(71), stout, oblong, and pointed at both ends, is 
separated from the rest by an interval, and that the mucus-canal does not extend 
on to it, but stops short at the preceding little tubular ossicle. Observe also the 
supratemporal range (7) following the direction of the dorsal fin, and extending along 
the upper side of the upper eye like a pseudo-suborbital range for it. The “turbinal,” 
or os terminale (1), is also seen, and above it, lying on the top of the head, is seen the 
corresponding ossicle of the eyeless side (19). On the eyeless side (fig. 2) observe the 
supratemporal range (7), following the direction of the dorsal fin; and the suborbital 
range, lying on the cheek higher up than the corresponding range on the other side, but 
with no eye visible in relation to it. On the top and front of the snout is again seen 
the turbinal (x) of this side. The anterior suborbital of the ocular side is a stout oblong 
bone, pointed at both ends, and artieulated to a process (+) of the prefrontal, opposite 
the olfaetory foramen, and is also closely related to the anteriorly projecting process of 
the palate-bone. As already stated, it is not perforated by any mucus-canal. That of 
the eyeless side (5, fig. 2) is similarly related to the corresponding prefrontal and 
palate-bones, but is smaller, flatter, and perforated by the mucus-canal, which traverses 
the rest of the range. The turbinal of the ocular side is larger than the opposite one, is 
curved, flattened, and contains a branching canal. All the rest of the superficial face- 
bones of the Halibut are very delicate tubules, often showing lateral branchlets, through 
which little ducts pass to ramify in the skin and open on its external surface. As they 
get smaller towards the ends of the several ranges, they often cease to be complete tubes, 
and appear like little scales with the edges folded up. As to number, these little bones 
are apt to be irregular. The supratemporal ranges generally consist of from twenty-two 
to twenty-five ossicles each, and the suborbital of the ocular side of from seventeen to 
nineteen ; but two often supply the place of one. The suborbital range of the eyeless 
side, however, consists pretty constantly of nine bones—about one-half the number found 
on the opposite side. 
In the Plaice the arrangement has undergone a little modification (see diagram, 
Plate XXXIL fig. 3). The canal of the ocular side, as usual, extends between the eyes 
and ends in its turbinalossicle. The opereulo-mandibular, the suborbital, and the supra- 
temporal branches are on both sides, similar to those in the Halibut; and so is also the 
cross commissure. But as the interocular process of the frontal bone of the eyeless side 
1s non-developed (p.275), the main mucus-canal of that side no longer extends between 
the eyes, but stops short at the commissure. Anteriorly we find, to the inner side of the 
nasal fossa of the eyeless side, a minute turbinal ossicle, containing as it were à little 
follicle, with two openings on the skin, this little mucus-cavity being in fact the remnant 
int € ~ of the eyeless side, but. detached altogether from the rest by the atrophy 
eg e of the intermediate portion. (For more details I refer the rea 
Tin BAL ^. gs. 3 and 4, and to the diagram, Plate XXXII. fig. 3.) | 
arrangement prevails in the genus Platessa, the interocular portion of the mucus 
