Herrick, Nerves of Siluroid Fishes. 227 
which it transverses in the usual way. The latter bone is very 
slender, scarcely more than an investment of the canal, and for 
its entire length is firmly ankylosed to the hyomandibular. 
The operculum and interoperculum, on the other hand, are 
freely moveable. 3 
Upon comparison of this specimen with those examined 
microscopically it would appear that the union of the opercular 
canal with the main canal is typical for this species, and that 
the failure to connect in the case of the specimen plotted is due 
to retardation of development or to some other exceptional 
cause. The cheek line of pit organs shown on the figure be- 
tween the opercular canal and the sub-orbital canal was observed 
also in a large specimen of A. nebulosus. It is represented on 
the plot (Fig. 1) by the last five or six of the large pit organs 
accompanying the opercular canal. These all lie dorsally of 
the canal, the caudal end of the line farther dorsal, but not ele- 
vated so far as in the specimen shown in Fig. 14. That is, in 
the specimen plotted the cheek line of pit organs is not so 
obliquely placed, but more nearly parallel with the opercular 
canal. 
Amewurus nebulosus, LESUEUR. This is the A. catus of 
most authors, but not of LINNAEus, the latter’s type being prob- 
ably the channel cat of the Potomac (A. albidus, JORDAN), ac- 
cording to JORDAN and EvermAnNn. Thecourses of the lateral 
canals of the head were dissected out in two small adults from 
20 to 30 cm. long. Without going into the details of the 
sense organs and pores, it may be said at once that the arrange- 
ment is in general as I have described it above for A. melas. 
The infra-orbital canal arises at a pore which lies very close to 
the second supra-orbital pore (the two pores opening within 2 
mm. of each other behind the anterior nasal aperture) but the 
supra-orbital and infra-orbital canals do not anastomose in my 
specimens as COLLINGE describes and figures (’95, Plate XVIII, 
Fig. 2) for this species. These two canals join within the 
frontal bone and the supra orbital is continued backward to end 
at a pore corresponding in position to pore V supra-orbital of 
my figure of A. melas. Surface examination shows that there 
