A34 ADIs: [Vor. XIV. 
origin (Nos. 36, 37); and sometimes wholly wanting (No. 13, p. 
242). In no teleost is it known to be traversed by an anterior 
cross-commissure of the lateral-line canals, that commissure, 
as a canal, not existing in teleosts, so far as I can find described. 
There is, however, in some teleosts, an anterior cross-commis- 
sure of surface sense organs, corresponding exactly, in its rela- 
tions to the canals of the lateral line system, to the commissural 
canal of Amia (No. I, p. 471); and in those fishes in which I 
definitely know this commissure to be found it is, with one appar- 
ent exception, Amiurus, associated with a purely dermal eth- 
moid. Sketches that I have, made several years ago, show it in 
Salvelinus namaycush and in Salmo fontinalis; and in Salmo 
salar, a fish so closely related to these two that it must be found 
in it also, there is, underlying the region where the line should 
be found, a purely dermal bone, the supra-ethmoid of Parker’s 
descriptions (No. 26). A similar bone is found in MWicropterus 
salmotdes (No. 41, p. 60); and in MMicropterus dolomieu my 
sketches show a cross-commissure of surface organs. In 
Amturus catus and Stlurus glanis my sketches show, on each 
side of the head, surface organs which represent the proximal 
parts of a cross-commissure, if not the entire commissure; and 
in Amiurus, McMurrich says of the mesethmoid that it “is one 
of the two bones in which the ossification of the cartilage is not 
completed in the adult, the inner surface of the bone being 
lined with it’ (No. 24, p. 276). In Clarius, a fish somewhat 
related to Amiurus, there is, according to Bridge (No. 7, p. 600), 
a median, T-shaped, dermal ethmoid. 
In Salmo salar, the supra-ethmoid of Parker overlaps exter- 
nally the anterior ends of the frontals (No. 26, Pl. VII, Fig. 1). 
In Amia the ethmoid would naturally have a similar relation to 
the thin, anterior processes of the frontals if it were produced 
backward between the nasals so as to reach the former bones. 
In larvae of Salmo salar (No. 45, Fig. 37) the ethmoid seems to 
lie, as it does in the adult Amia, considerably in front of the 
frontals. 
In Esox luctus I find bones 2 of Huxley’s descriptions (No. 21, 
p. 134) lying immediately beneath lines of surface sense organs, 
which are somewhat longitudinal in direction and do not form a 
