THE SENSORY CANAL SYSTEM OF FISHES. 529 
traces of a rudimentary or degenerate canal in the pre-oper- 
culum. 
The system in Calamoichthys is practically the same as 
that described in Polypterus. 
The family Am11p# has been the most thoroughly studied of 
any of the Teleosteoid Ganoids (1). The branching of the 
lateral canal still persists in the posterior border of the scale, 
the canals of the head are almost wholly contained in the bones, 
dermal portions being exceedingly small. The cluster and 
primitive pores are much more specialised in character and 
fewer in number. There is little or no branching of the 
system upon the head, excepting in the pre-operculum, an 
operculo-mandibular branch being present. There is no con- 
nection between the two mandibular portions in the median 
symphysis of the lower jaw. Both occipital and ethmoidal 
commissures are present, and a similar form of branching in 
the pre-orbital region as was noticed in Polyodon. 
Not a few writers have examined the sensory canal system 
with a view to ascertaining its value in classification. I am 
not aware that it has been used for such purposes, and from 
the variability of its nature I should much doubt its value if 
applied in any than a very general manner. 
xv. CLASSIFICATION. 
GANOIDEI. 
Group 1. Srnacuorpet, Bridge. 
Sub-order 1. CnHonproste1, Miiller. 
Fam. i. PoLyoponTip. 
Polyodon, Lacép. 
— folium, L., p. 507. 
Psepherus. 
—  gladius, Martens, p. 519. 
Fam. 11. ACIPENSERIDA, 
Acipenser, Artedi. 
—  sturio, L., p. 521. 
Scaphirhynchus, Heckel, p. 528. 
— catephractus, Gray. 
