230 JouRNAL OF COMPARATIVE NEUROLOGY. 
doubtless the specimens of Ameiurus catus which COLLINGE 
examined exhibited a similar peculiarity, for he says that the 
canal in that species runs through the external portion of the 
hyomandibular, a form of statement which is hardly admissible 
in view of the fact this bone belongs to the primordial cranium. 
In CoriincGe’s description he adds that from the preoperculum 
the canal ‘‘passes into the distal portion of the quadrate and 
then into the mandible.”’ It is obvious in all of the forms 
which I have examined that the canal has no relation to the 
quadrate, though in this instance the preoperculum, quadrate 
and hyomandibular are very intimately joined. The course of 
the canals in front of the eye was not dissected out. 
Ictalurus punctatus, Ra¥. The heads of two large spect- 
mens of this species were partially dissected and the arrange- 
ments so far as studied correspond quite closely with those just 
described for Leptops. The head is much narrower and higher 
than in Leptops and the preopercular bone extends much 
farther dorsally so that the opercular canal is enclosed in this 
bone for about three fourths of the distance between the squa- 
mosal bone and the mandible, instead of less than one half, as 
in Leptops. From the post-temporal bone the main canal 
passes into the squamosal without being enclosed by a separate 
ossicle. Within the squamosal bone the opercular canal joins 
the main canal and, as before, passes for a short distance 
through this bone, directed forward, outward and downward 
toward the operculum. In the interval, in my specimens about 
I cm., between the squamosal and the dorsal tip of the pre- 
operculum the canal is enclosed by a single very slender supra- 
opercular ossicle. The remainder of the canal is deeply em- 
bedded in the preoperculum nearer its cephalic than its caudal 
margin. As in Leptops, the preoperculum is immovably co- 
osified with the quadarate and the hyomandibular for its entire 
length. The operculum and interoperculum, on the other 
hand, are freely movable. 
Noturus flavus, Rar. Two examples of this species about 
18 cm. long were dissected. The opercular canal is connected 
with the main canal, enclosed by one or more slender tubular 
