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 suboperculum 

 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 G-egenbaur 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 branchiostegal rag, and the operculum and inter- 

 operculum correspond to another rag which has become divided 

 transversely. 



IV.— THE BRANCHIAL APPARATUS. 



This consists of five arches, each 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 hgpobran- 

 ■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 phargngo-branchial, 

 lies near the median line of the roof of the pharynx. 



In Amiurus (PI. II. Fig. 3) all the arches do not possess the typi- 

 cal number of bones. Only two copula? are present, i. e., those be- 

 tween the 1st and 2nd (cpj), and 2nd and 3rd arches (cp. 2 ) ; between 

 the 3rd and 4th a cartilage (c/> 3 . 4 ) is present, with the posterior ex- 



