Herrick, Nerves of Silurotd Fishes. 219 
r. mandibularis externus facjalis and which clearly resemble 
the similar organs on the operculum and mandible of Menidia 
and many other teleosts. I have found no organs in the cat 
- fish corresponding to those on the operculum innervated by the 
r. opercularis superficialis VII in Menidia. 
On the right side of the specimen figured the relations of 
the opercular canal are somewhat different. The preoperculum 
extends somewhat farther dorsally and the canal runs out from 
its tip toward the main canal, terminating by a pore very near 
to the first pore of the main canal, which runs out through the 
squamosal bone. There is, however, no communication with 
the main canal. This long portion of the opercular canal which 
extends dorsad and caudad from the end of the preoperculum 
runs close under the skin and is enclosed in a very slender tu- 
bular ossicle which articulates to the free end of the preopercu- 
lum and Hes embedded in the dermis, separated from the under- 
lying hyomandibular bone by muscle. Its dorsal end is free. 
In two other specimens of which I have transverse sections 
the relations are still different. In these specimens the arrange- 
ments are the same as in the one figured except at the caudal 
end of the opercular canal, which joins the main canal between 
the first and second sense organs within the squamosal bone. 
The preoperculum extends much farther dorsally than in the 
other case and the canal extends dorsally and caudad from it 
with no bony investment, embedded in the dermis, to a wide 
pore by which it commuicates with the surface about midway 
between the preoperculum and the squamosal. This is a double 
pore corresponding to pore ZX operculo-mandibular and pore / 
of the main canal of Fig. 1. Between this pore and the squa- 
mosal the canal is invested by a feebly ossified incomplete bony 
ring which is unconnected with any other bone save the squa- 
mosal at its dorsal end. The course of the canal between the 
preoperculum and the squamosal in these two specimens is indi- 
cated on Fig. 1 by dotted lines. 
The slender investing bones enclosing the opercular canal 
between the preoperculum and the squamosal are the supra- 
opercular bones, termed by Agassiz the supra-temporale, but 
