292 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
it lies on the inner surface of the interoperculum, and its outer por- 
tion lies below and slightly behind the operculum. Accordingly as 
above stated, it may be considered as equivalent to the subopereculum 
of other Teleosts. The operculum and interoperculum seem to have 
been originally a single ray, which dividing transversely, gave rise to 
the two bones. They are directly in apposition in Amiurus, the lower 
extremity of the operculum being of the same size as the upper (pos- 
terior) extremity of the interoperculum. With regard to the attach- 
ment of the latter to the articulare, it may be stated that it is just as 
firmly attached to the epihyal, which, however, it overlaps, and it is 
possible that it may, as Gegenbaur suggests, be the only remaining 
ray of the mandibular arch. However, be that as it may, it is evi- 
dently an appendage of a visceral arch, and as such, is homologous 
with a branchiostegal ray. 
My conclusions as to the homologies of the opercular bones are as 
follows :—The preoperculum is developed around a mucous canal and 
does not belong to the same category as the other bones. The suboper- 
culum is a modified brunchiostegal ray, and the operculum and inter- 
operculum correspond to another ray which has become divided 
transversely. 
IV.—THE BRANCHIAL APPARATUS. 
This consists of five arches, gach arch consisting of a number of 
bones, the upper portion of each being bent at an acute angle, so as 
to lie in a plane almost parallel to that of the lower portion. In 
other words, the lower portions of the arches lie on the floor of the 
pharynx, the upper portion in its roof. In a typical arch five por- 
tions are present. Below in the middle line, extending between the 
arch and its successor, is an impair bone, the copula. Opposite the - 
anterior end of the copula is a usually short portion —the hypobram- 
chial, on the outer side of which lies the ceratobranchial, usually the 
largest of the branchial elements. Between the last-named portion 
and its successor, the epibranchial, the bend occurs, so that the ex- 
tremity of the arch, formed by a usually small pharyngo-branchial, 
lies near the median line of the roof of the pharynx. 
In Amiurvs (Pl. II. Fig. 3) all the arches do not possess the typi- 
cal number of bones. Only two copulxz are present, 7. e., those be- 
tween the lst and 2nd (cp,), and 2nd and 3rd arches (cp,) ; between 
the 3rd and 4th a cartilage (cp,,) is present, with the posterior ex- 
