226 JOURNAL OF COMPARATIVE NEUROLOGY. 
The discrepancies in the descriptions above referred to and 
also uncertainty in my own mind as to the true significance of 
the small ossicle which I find in A. melas between the 
squamosal and the post-temporal have led me to examine these 
features in such North American Siluridae as are available. A 
number of the North American cat fishes were examined by 
dissection as follows: 
Amewsrus melas, JORDAN and Corre. This dissection of a 
large specimen of the species used for the microscopical study 
was made for purposes of control. The specimen, which was 
14 cm. long, was examined with a hand-lense, and all of the 
pores of the canals located. The arrangements of these is in- 
dicated in the sketch (Fig. 14), as well as the positions of some 
of the large pit organs, though not all of the latter could be 
definitely fixed, especially in the less pigmented areas. The 
lateral canal of the trunk runs as far back as the level of the 
ventral fins. Behind this there are more obscure indications of the 
lateral line, suggesting that the sense organs extend still farther, 
though even these indications disappear before the base of the 
tail fin is reached. Behind the shoulder girdle there is but one 
tubular ossicle (corresponding to the bone Z.OS. 7 of the 
sections), and that feebly developed. The lateral line ossicle in 
front of the girdle (ESC.) appears exactly as I find it in the 
sections. There is no occipital commissure of the canal sys- 
tem, and the two large pit organs forming the middle pit line 
(Fig. 14, w. /.) are found in their proper positions. 
The opercular canal joins the main canal in the squa- 
mosal bone. From the point of union it runs downward and 
forward, passing directly from the squamosal into a well devel- 
oped tubular ossicle (supra-opercular bone) which is long and 
very slender, but firmly ossified, lying under the skin and over 
the muscles. The double pore (/ of the main line and LX of 
the operculo-mandibular) opens immediately beyond this ossi- 
cle, and the canal continues in the same direction as before 
without osseous support. This membranous portion crosses the 
head of the opercular bone, where it articulates upon the 
hyomandibular, and enters the dorsal tip of the preoperculum, 
